Biosensors and methods of preparing same

ABSTRACT

A biosensor strip having a low profile for reducing the volume of liquid sample needed to perform an assay. In one embodiment, the biosensor strip includes an electrode support; an electrode arrangement on the electrode support; a cover; a sample chamber; and an incompressible element placed between the cover and the electrode support, the incompressible element providing an opening in at least one side or in the distal end of the sample chamber to provide at least one vent in the sample chamber. In another embodiment, the biosensor strip has an electrode support; an electrode arrangement on the electrode support; a cover; and a sample chamber, the cover having a plurality of openings formed therein, at least one of the openings in register with the sample chamber. The invention further includes methods for preparing such a biosensor strips in a continuous manner.

This application is a continuation-in-part application of co-pendingapplication having Ser. No. 11/147,532, filed Jun. 8, 2005, the entiredisclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to biosensor strips and methods for preparingbiosensor strips.

2. Discussion of the Art

An electrochemical cell is a device that has a working electrode and acounter electrode, which electrodes are connected to one anotherelectrically. When in use, electrochemical reactions occurring at eachof the electrodes cause electrons to flow to and from the electrodes,thus generating a current. An electrochemical cell can be set up eitherto harness the electrical current produced, for example in the form of abattery, or to detect electrochemical reactions which are induced by anapplied current or voltage.

A biosensor is a type of electrochemical cell, in which the electrodearrangement has a working electrode, a reference electrode, and acounter electrode (or in place of the reference electrode and counterelectrode, an electrode that functions as both reference electrode andcounter electrode). Reagents, e.g., enzyme and mediator, that arerequired for generating a measurable signal upon electrochemicalreaction with an analyte in a sample to be assayed, are placed over theworking electrode so that the reagents cover at least a portion of thesurface of the working electrode.

In other cases, the biosensor includes a reference electrode having, forexample, a mixture of silver and silver chloride. The reagents areplaced over at least the working electrode. However, placing thereagents over the reference electrode will not influence theelectrochemical measurement at the working electrode. For example, areagent containing a quinone mediator would not react with thesilver/silver chloride mixture. A biosensor having this type of mediatormakes it possible for reagents to be applied over the working electrodewith inaccurate registration of the reagent relative to the workingelectrode.

In still other instances, the reagents of the biosensor are required tobe isolated from substances applied to the reference electrode in orderto prevent interaction between the mediator and the substances appliedto the reference electrode. In these cases, precise registration of thereagents on the working electrode may be required.

The differences between the various types of biosensors are dependentupon the chemical reaction desired. One of ordinary skill in the art canreadily modify a given biosensor so as to render it capable ofperforming the desired chemical reaction.

U.S. Pat. No. 6,863,800, incorporated herein by reference, shows abiosensor strip 10 that contains an electrode arrangement that issuitable for use in this invention. Referring to FIG. 1 of U.S. Pat. No.6,863,800, an electrode support 11, an elongated strip of polymericmaterial (e.g., polyvinyl chloride, polycarbonate, polyester, or thelike) supports three tracks 12 a, 12 b and 12 c of electricallyconductive ink, such as carbon (e.g., carbon particles). These tracks 12a, 12 b and 12 c determine the positions of electrical contacts 14 a, 14b and 14 c, a reference electrode 16, a working electrode 18, and acounter electrode 20. The electrical contacts 14 a, 14 b and 14 c areinsertable into an appropriate measurement device (not shown).

Each of the elongated portions of the conductive tracks 12 a, 12 b and12 c can optionally be overlaid with a track 22 a, 22 b and 22 c ofconductive material, such as a mixture including silver particles andsilver chloride particles. The enlarged exposed area of track 22 boverlies the reference electrode 16. A layer of a hydrophobicelectrically insulating material 24 further overlies the tracks 22 a, 22b and 22 c. The positions of the reference electrode 16, the workingelectrode 18, the counter electrode 20, and the electrical contacts 14a, 14 b and 14 c are not covered by the layer of hydrophobicelectrically insulating material 24. This layer of hydrophobicelectrically insulating material 24 serves to prevent short circuits.The layer of hydrophobic electrically insulating material 24 has anopening 26 formed therein. This opening 26 provides the boundary for thereaction zone of the biosensor strip 10. Because this layer ofinsulating material is hydrophobic, it can cause the sample to berestricted to the portions of the electrodes in the reaction zone. Theworking electrode 18 includes a layer of a non-reactive electricallyconductive material on which is deposited a layer 28 containing aworking ink for carrying out an oxidation-reduction reaction. At leastone layer of mesh 30 overlies the electrodes. This mesh layer 30protects the printed components from physical damage. The mesh layer 30also helps the sample to wet the electrodes by reducing the surfacetension of the sample, thereby allowing it to spread evenly over theelectrodes. A cover 32 encloses the surfaces of the electrodes that arenot in contact with the electrode support 11. This cover 32 is a liquidimpermeable membrane. The cover 32 includes a small aperture 34 to allowaccess of the applied sample to the underlying mesh layer 30. Thebiosensor strip of FIG. 1 is a top-fill biosensor strip, in which thesample wicks to the electrodes via a layer of mesh. FIG. 2 of U.S. Pat.No. 6,863,800 shows an end-fill biosensor strip that does not have amesh layer. The sample reaches the electrodes via capillary attraction.The biosensor strip 10′ of FIG. 2 employs a cover layer 40 and a spacerlayer 42, e.g., a layer of adhesive, between the electrode support 11and the cover layer 40. The adhesive can be a pressure-sensitiveadhesive. The cover layer 40 does not have an aperture. The spacer layer42 has a slot 44 that provides the boundary of the reaction zone. Theliquid sample enters the biosensor strip 10′ via an opening 46 formed atone end of the slot 44 at one end of the biosensor strip 10′. The liquidsample is introduced at the opening 46 and reaches and traverses thereaction zone by means of the action of capillary force.

Application of the cover 32 to the layer of insulating material 24 iscurrently achieved by aligning the cover above the remaining componentsto be processed and then clamping the cover 32 to the aforementionedremaining components together with a flat platen and a profiled block.The flat platen is placed below the electrode support 11 and theprofiled block is placed above the cover 32. The profiled block isheated prior to the step of laminating the cover 32 to the remainingcomponents of the biosensor strip.

FIG. 1, of this disclosure herein, shows how the flat platen “P” and theheated, profiled block “B” are aligned during the laminating step.Ensuring that the profiled block “B” is properly aligned with the platen“P” is essential for the success of the process. Proper alignmentrequires a relatively high degree of skill and considerable time toachieve the bond required for preparing the biosensor strip “S”.Although this method produces an excellent bond, it may also cause adome to form in the tape between the points where the portions of theprofiled block contact the cover 32. The formation of this domeincreases the volume of the electrochemical cell unnecessarily. FIGS.2A, 2B and 2C herein illustrate graphically how dome cross sections,dome radii, and dome heights of singulated biosensor strips preparedwith the flat platen “P” and heated profiled block “B” that is currentlyused to prepare biosensor strips vary as a function of width of thesample chamber.

In addition, the method of application currently used to prepare thebiosensor strip is an intermittent process, i.e., lamination of thecover to the remaining layers is not carried out continuously.Accordingly, the method of lamination currently used requires thecomponents to be laminated to be indexed to the proper position, havetheir motion halted at precisely the proper moment, clamped together,and then held together for a specified period of time as the heattransfers from the profiled block, through the backing of the cover andinto the layer of adhesive. The clamp then has to be released and theproduct moved out of the way. Furthermore, reactivating or softening theadhesive while the layer of tape is clamped onto the remaining layersbrings about the transfer of a great deal of heat into the remaininglayers. Because enzymes are denatured at elevated temperatures, a highlevel of heat transfer is not desirable.

Reduction in the volume of the electrochemical cell by removing the domecaused by the process employing the platen and profiled block used toadhere the cover to the remaining components of the biosensor strip canbe brought about by using a low-profile tape for preparing the cover. Alow-profile tape can reduce the volume of the sample chamber by 33%. Theneed to reduce the volume of the sample chamber is driven by theperception that if a lower quantity of blood is required to carry out atest, then a lower amount of pain is experienced by the patient toobtain the required quantity of blood. Previous trials of low-profiletapes that use pressure-sensitive adhesive (PSA) have been known to failwhen the cards on which a plurality of the biosensors are printed areconverted into individual biosensor strips. The PSA builds up on thecutters of the converting machines, e.g., a packaging machinecommercially available from Romaco Siebler and having the tradename“SIEBLER”. This buildup results in the adhesive's falling in lumps intothe packaging of the biosensor strips and also requires extensivecleaning of the cutter blades and undercarriage of the convertingmachine.

It is also known that sample chambers in biosensor strips need means forair to escape as liquid displaces it. In many products, these means areprovided by a single vent opening (see reference numeral 34), in eitherthe upper or lower surface of the biosensor strip, which means that thesingle vent opening requires proper registration in two directions toprovide a reproducible and reliable biosensor strip. In other words, ifthe vent opening is misaligned in a direction perpendicular to thedirection of sample flow, liquid will not enter the sample chamber; ifthe vent opening is misaligned in a direction parallel to the directionof sample flow but is still in register with the sample chamber, liquidwill enter the sample chamber, but the quantity of sample may beinsufficient to trigger the assay or perform the assay correctly; if thevent opening is misaligned in a direction parallel to the direction ofsample flow but is not in register with the sample chamber, liquid willnot enter the sample chamber.

As indicated previously, the cover can be adhered into place by a methodemploying a platen and a profiled block. As also indicated previously,this method creates a dome, which is open to the surrounding environmentat the distal end of the sample chamber. This opening provides a naturalvent, but increases the volume of sample required to fill the samplechamber. The low-profile tapes often bond so well that no air can escapefrom the sample chamber, and, consequently, the sample will not flowinto the sample chamber. Forming an opening in the distal end of thesample chamber allows the air to escape from the sample chamber and thesample to enter the sample chamber. Forming an opening in the distal endof the sample chamber would also aid the flow of a sample in the samplechamber wherein flow is driven by capillary attraction (see FIG. 2 ofU.S. Pat. No. 6,863,800) or by wicking along a layer of mesh, e.g.,chemically assisted wicking.

Forming various vents in the sides of the sample chamber has beenattempted, but all such vents result in an unsightly mess as the liquidsample wicks along the vent. Vents formed by perforation techniquescomprise one opening in the cover of the biosensor strip. The liquidsample does not wick into the opening formed in the cover. However, asstated previously, a vent formed in the cover requires properregistration in two directions.

The problem of variability of fill rate from biosensor strip tobiosensor strip is believed to be caused by adhesive flow and the use ofever finer meshes, thereby resulting in a seal being formed between thecover and the layer of insulating material. The use of fine meshesreduces the quantity of liquid sample, e.g., blood, needed to perform anassay. However, the use of fine meshes also results in a smoothersurface in the insulating layer. The method currently used for preparingbiosensor strips, i.e., laminating by means of the flat platen andprofiled block, encourages the sample chamber to seal if too muchadhesive flows during the lamination process. The degree of sealingdirectly affects the rate at which a liquid sample fills the samplechamber. A reliable and reproducible vent is required to ensure minimalvariation in fill rate.

In view of the foregoing, it is desired to develop a biosensor striphaving a low profile in order to reduce the volume of liquid samplerequired to perform an assay. It is further desired to develop a meansfor venting such a low-profile biosensor strip. It is further desired todevelop a method for preparing such a biosensor strip in a continuousmanner. It is still further desired that this biosensor strip bereproducible and reliable with respect to filling with liquid sample.

SUMMARY OF THE INVENTION

In one aspect, this disclosure provides a biosensor strip fordetermining the concentration of an analyte in a sample of liquid, thebiosensor strip having an electrode support, an electrode arrangement onthe electrode support, a cover, a sample chamber, and an incompressibleelement in contact with the cover, the incompressible element providingan opening in at least one side or in the distal end (e.g., inlet end)of the sample chamber to provide at least one vent in fluidcommunication with the sample chamber.

In another aspect, this disclosure provides a biosensor strip fordetermining the concentration of an analyte in a sample of liquid, thebiosensor strip having an electrode support, an electrode arrangement onthe electrode support, a cover, and a sample chamber, the cover having aplurality of openings formed therein, at least one of the openings inthe cover in register with the sample chamber. In an alternativeembodiment of the second aspect, instead of openings being formed in thecover, the electrode support can have a plurality of opening formedtherein, the openings being in register with the sample chamber.

By forming a plurality of openings in the cover or in the electrodesupport, in use, a liquid sample will fill such a biosensor strip evenif during the manufacturing process adhesive on the cover flowsexcessively during the process of sealing the cover to the remainingcomponents of the biosensor strip. The aforementioned biosensor stripscan have at least one layer of mesh is interposed between the cover andthe sample chamber.

The biosensors strips of this disclosure, whether having anincompressible element or a plurality of openings in the cover or theelectrode support, are particularly suited for using a reduced samplevolume less than about 1 microliter, e.g., less than about 0.3microliters, e.g., less than about 0.2 microliters, e.g., less thanabout 0.1 microliter to determine an analyte concentration, such as aglucose concentration. The biosensor strips are also particularly suitedfor fast analyte concentration determination. Many times, the analyteconcentration is determined within about 1-10 seconds (e.g., about 5-10seconds) after filling the sample chamber with liquid sample (e.g.,blood) to be analyzed. In some embodiments, the time to determineanalyte concentration is less than about 5 seconds (e.g., about 3-5seconds) or less than about 3 seconds (e.g., about 1-3 seconds).

The biosensors of this disclosure can be uses in a system to determinethe concentration of an analyte in a sample, the system including atleast one biosensor and a meter operably connectable to the biosensor.

In another aspect, this disclosure provides a continuous method ofapplying a cover having a backing bearing a layer of an adhesive on onemajor surface thereof to the remaining components of a biosensor strip.In this method, the cover is formed from segments of a tape having abacking having a layer of adhesive on one major surface thereof. Thecover can be applied by providing a row containing a plurality ofuncompleted biosensor strips; providing a tape having a backing bearinga layer of adhesive on one major surface thereof feeding the row into atape application apparatus, e.g., a laminator; feeding the tape into thetape application apparatus, e.g., laminator; applying the tape to therow, e.g., by lamination, whereby the row contains a plurality ofcompleted biosensor strips; and singulating the row of completedbiosensor strips to provide a plurality of individual biosensor strips.

When using a hot melt or heat activatable adhesive, the method can beused to adhere the aforementioned cover to the remaining components ofthe biosensor strip by preheating the backing and the adhesive by meansof conduction through contact with either a stationary or a movingsource of heat. The source of heat is typically a good conductor of heatand is controlled to achieve a temperature that will melt, or soften,the adhesive, but will not significantly damage the backing of thecover. The tape can either remain stationary in the heat applicationzone of the tape application apparatus, e.g., laminator, with nodetrimental effect to the backing, to the adhesive, or to the remainingcomponents of the biosensor strip, or, alternatively, the tape can movecontinuously in the heat application zone of the tape applicationapparatus, e.g., laminator, whereby there will be no detrimental effectto the backing, to the adhesive, or to the remaining components of thebiosensor strip.

After the tape is heated, the tape is applied to the remainingcomponents of the biosensor strip, such as by a pressure roller, priorto the tape being cooled to a temperature below the hardening point ofthe adhesive. Tapes applied in such a manner typically exhibit a muchlower profile than do those tapes applied by adhesive reactivation insitu. The tapes applied according to the method of this invention alsohave the potential to be processed much more quickly than do tapesapplied in situ. At most, only an insignificant amount of the samplewicks along the surface of the incompressible element of the biosensorstrip. Furthermore, this wicking occurs at a very slow rate.

When using a pressure-sensitive adhesive, a tape application apparatusemploying heat to melt or soften the adhesive would not be used. A tapeapplication apparatus equipped with pressure rollers can be used toapply a tape having a backing having a layer of pressure-sensitiveadhesive to the uncompleted biosensor strips. The steps subsequent toapplying the tape to the uncompleted biosensor strips would besubstantially similar to those steps subsequent to applying the tapeemploying a hot melt adhesive to uncompleted biosensor strips.

Regardless of the type of adhesive used to adhere the tape to theremaining components of the biosensor strips, this disclosure providesseveral methods for introducing vents in the biosensor strips. A methodfor forming openings in the cover of a biosensor strip, which openingsrequire registration in only one direction, is provided. This methodsimplifies the provision openings in the cover. According to thismethod, small openings that function as vents can be provided in a tapeby preparing the cover by a laser or by mechanical piercing. Theopenings could be formed in a line and could be separated by specified,typically regular, intervals. The intervals can be selected to ensurethat at least one opening, and typically more than one opening, is aboveeach sample chamber after the tape is applied to the remainingcomponents of the biosensor strip, the remainder of the openingsbecoming redundant. By employing openings formed in this fashion, one ofthe two directions of registration is no longer necessary, therebypotentially leading to higher production rates and more accuratepositioning of at least one vent in the cover of the biosensor strip. Inan alternative embodiment, openings can be formed in the electrodesupport, rather than in the cover of the biosensor strip. More accuratepositioning of the tape from which the cover is formed is achieved in acontinuous method because the tapes can be maintained under a steadystate of tension, thereby rendering the tapes easier to control andposition than those tapes subject to intermittent, i.e., stop/startmethods, where tension continually increases and decreases.

This disclosure further provides a method for introducing at least oneopening in at least one side of the sample chamber or in the distal end(e.g., inlet end) of the sample chamber of the biosensor strip, ratherthan in the cover or in the electrode support. This method simplifiesthe provision of vents in the sample chamber. According to this method,small openings that function as vents can be provided by a substantiallyincompressible element, such as, for example, a thread, a ribbon, or atape. At least one vent, in one side of the sample chamber or in itsdistal end, can be formed by providing a row containing a plurality ofuncompleted biosensor strips; providing a tape having a backing bearinga layer of adhesive on one major surface thereof; providing a length ofmaterial suitable for forming incompressible elements; combining thetape and the length of material for forming incompressible elements,whereby the tape and the length of material for forming theincompressible elements form an assembly; feeding the row into a tapeapplication apparatus, e.g., a laminator; feeding the assembly into thetape application apparatus, e.g., laminator; applying the assembly tothe row, e.g., by lamination, whereby the row contains a plurality ofcompleted biosensor strips; and singulating the row of completedbiosensor strips to provide a plurality of individual biosensor strips.If the adhesive is a hot melt adhesive, the tape is preheated on a tapeapplication apparatus prior to being combined with the incompressibleelement, and the resulting combination of the tape and incompressibleelement applied to the remaining components of the biosensor strip. Ifthe adhesive is a pressure-sensitive adhesive, there is no need topreheat the tape on a tape application apparatus prior to combining thetape and the incompressible element and applying the resultingcombination to the remaining components of the biosensor strip. Byemploying openings generated in this fashion, inexpensive and readilyavailable materials can be applied concurrently with the cover-formingtape at high production rates and with a high degree of accuracy.

The methods described herein do not require difficult settings forcarrying out the procedures. The methods of this disclosure are suitablefor preparing biosensor strips that utilize a reduced volume, e.g., lessthan about 0.3 microliters, e.g., less than about 0.2 microliters, e.g.,less than about 0.1 microliter, of the sample chamber of the biosensorstrip by removing the dome over the sample chamber, which results fromthe conventional strip manufacturing process. The methods describedherein can be embodied in a continuous process, thereby increasingoutput and bringing about greater uniformity of biosensor strips.

Because the methods described herein that involve heating the tape thatforms the cover introduce the heat prior to contacting the tape with theremaining components of the biosensor strip, heat input to the resultingproduct is greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cross section of the flat platen and theheated profiled block that is currently used to prepare biosensorstrips. The views also show the cross section of the dome of thebiosensor strip that is produced when the flat platen and heated,profiled block are used to join the cover to the remaining components ofthe biosensor strip.

FIGS. 2A, 2B and 2C are graphs relating to dome cross sectional area,dome radii, and dome heights of biosensor strips prepared with the flatplaten and heated profiled block that is currently used to preparebiosensor strips. In FIGS. 2A, 2B and 2C, the sample chamber of thebiosensor strip described as having a narrow sample chamber has a widthof 1.5 mm, the sample chamber of the biosensor strip described as havinga medium sample chamber has a width of 2.8 mm, and the sample chamber ofthe biosensor strip described as having a wide sample chamber has awidth of 4.1 mm.

FIG. 3 is an exploded view of a biosensor strip according to oneembodiment of this disclosure. In this embodiment, a layer of mesh isabsent from the biosensor strip.

FIG. 4 is a cross-sectional view of the biosensor strip of FIG. 3showing an incompressible element that forms a vent in the side of thesample chamber.

FIG. 5 is an exploded view of a biosensor strip according to anotherembodiment of this disclosure. In this embodiment, a layer of mesh ispresent in the biosensor strip.

FIG. 6 is a cross-sectional view of the biosensor strip of FIG. 5showing an incompressible element that forms a vent in the side of thesample chamber.

FIG. 7 is an exploded view of a biosensor strip according to anotherembodiment of this disclosure. In this embodiment, a layer of mesh isabsent from the biosensor strip.

FIG. 8 is an exploded view of a biosensor strip according to anotherembodiment of this disclosure. In this embodiment, a layer of mesh ispresent in the biosensor strip.

FIG. 9 is a schematic diagram of a prototypical laser that can be usedto form openings in a tape for forming the cover of a biosensor strip.

FIG. 10 is a schematic diagram showing a side view in elevation of onetype of apparatus that can be used to prepare biosensor strips of thisdisclosure.

FIG. 11 is a schematic diagram showing a side view in elevation ofanother type of apparatus that can be used to prepare biosensor stripsof this disclosure.

FIG. 12 is a schematic diagram showing a top plan view of the apparatusof FIG. 11.

FIG. 13 illustrates the testing set-up for analyzing burrs in thevicinity of an opening formed by a laser in a tape for forming covers ofbiosensor strips.

FIG. 14 illustrates a row of non-singulated biosensor strips used fortesting the accuracy of an apparatus for applying tape to a row ofuncompleted biosensor strips.

DETAILED DESCRIPTION

As used herein, the phrase “sample chamber” means a volume for thereceipt of liquid to be analyzed, the chamber having a proximal endwhere a liquid sample is introduced into the sample chamber, a distalend toward which the liquid sample generally flows when it has beenintroduced into the sample chamber, a first side extending between theproximal end and the distal end of the sample chamber, and a second sideextending between the proximal end and the distal end of the samplechamber, the first side and the second side serving to retain the liquidsample in the sample chamber. The distal end of the sample chamber isthe “inlet” or “inlet end” into the sample chamber. The sample chamberis present between the electrode support and the cover, and includes atleast a portion of the electrode arrangement therein. The term “card”means a sheet of unconverted stock having a plurality of rows, each rowincluding a plurality of uncompleted biosensor strips that require acover to be applied to form a completed biosensor strip. The term “row”means a plurality of uncompleted biosensor strips arranged in a straightline with the sample chambers at one elongated side of the row and thecontacts at the other elongated side of the row. The phrase “uncompletedbiosensor strip” means a biosensor strip that is lacking a cover. Theuncompleted biosensor strip is a component of a row or card. The phrase“completed biosensor strip” means a biosensor strip that has a cover,but that is not singulated into an individual biosensor strip. Thephrase “individual biosensor strip” means a singulated biosensor striphaving a cover. In general, the phrase “biosensor strip”, when usedalone, means an individual biosensor strip. The phrase “low-profile”means without a substantial dome. The phrase “incompressible element”means a thread, ribbon, filament, layer, or the like that will not onlyresist compression by the methods of this disclosure used to apply thecover to the remaining components of the individual biosensor strip, butwill also resist compression during normal storage and use of thecompleted biosensor strip. The incompressible element need only resistcompression to the degree that the vent(s) formed by the element remainopen to the atmosphere. The term “filament” means any fine, elongatedfiber having a circular or substantially circular cross-section. Theterm “ribbon” means a narrow strip or band of material, typically madeof natural material or synthetic material. The term “dome” means theshape assumed by the cover of a biosensor strip when the biosensor stripis formed by the aligning/clamping/heating method currently employed toapply a cover to the remaining components of an uncompleted biosensorstrip. The dome is an elevated and redundant space above the samplechamber of the biosensor strip. The term “step” means a portion of thecover of a biosensor strip that is at a higher level than the remainingportion of the cover of the biosensor strip. The term “backing” meansthe layer of a tape that support a layer of adhesive. The term andphrase “laminator”, “laminating apparatus”, and the like, mean a machinethat positions and consolidates two or more substrates together. Morespecifically, the term and phrase “laminator”, “laminating apparatus”,and the like, include equipment for applying a cover to the remainingcomponents of an uncompleted biosensor strip. The term “vent” means anopening the passage of escape of a gas or vapor, e.g., air. The phrase“datum edge” means the edge of a row, card, or tape that is employed asthe positioned edge against a fixed guide. This is in contrast to theother edges of the row, card, or tape, which edges are handled withmoving guides, e.g., spring rollers, on account of acceptable supplytolerances. The phrase “windy miller” means a manually operated machinefor converting cards into rows. The phrases “row cutter”, “row cuttingdevice”, “row cutting assembly”, and the like, mean a machine forconverting rows of biosensor strips into narrower rows for the desiredbiosensor strip, e.g., a strip having a width of 40 mm to a strip havinga width of 34.5 mm. The term “singulated” refers to individual biosensorstrips cut from a row containing a plurality of biosensor strips. Thephrase “row convert”, or the like, means the process carried out by arow cutter. The phrase “slip ring” means a device that permits a numberof electrical channels to be transferred to a rotating component withouttwisting of connecting cables. The phrase “swash plate” means a rotatingelliptical element skewed from its axis such that it can act as adual-acting cam. The phrase “driven pin holder” means a device driven bythe swash plate, whereby the pin holder reciprocates. The term “bowing”refers to the curvature assumed by a card or row. The phrase “electrodearrangement” means a collection of electrodes placed in a specific orderor relation on an electrode support. Electrodes suitable for anelectrode arrangement for a biosensor strip for this disclosure arewell-known to those of ordinary skill in the art. In general, theseelectrodes comprise a working electrode and a counter electrode, andoptionally comprise any or all of a reference electrode, a triggerelectrode, and auxiliary electrodes. As used herein, the phrases“perforated from the adhesive side”, “forming openings from the adhesiveside”, and the like, mean that the laser beam passed through theadhesive side of the tape before passing through the backing side of thetape. The phrases “perforated from the backing side”, “forming openingsfrom the backing side”, and the like, mean that the laser beam passedthrough the backing side of the tape before passing through the adhesiveside of the tape.

Referring to the figures, FIGS. 3, 4, 5 and 6 illustrate a biosensorstrip 110 or 110′ having vents in the sides of the sample chamber. InFIGS. 4 and 6 and FIGS. 3 and 5, biosensor strip 110, 110′,respectively, has an electrode support 111, e.g., an elongated strip ofpolymeric material (e.g., polyvinyl chloride, polycarbonate, polyester,or the like) that supports three tracks 112 a, 112 b and 112 c ofelectrically conductive ink, such as carbon (e.g., carbon particles).One suitable source for conductive carbon ink is Asbury Carbons ofAsbury, N.J. Depending on the ink used, it may be combined with othermaterials to facilitate processing. These tracks 112 a, 112 b and 112 cdetermine the positions of electrical contacts 114 a, 114 b and 114 c, areference electrode 116, a working electrode 118, and a counterelectrode 120. Although not illustrated, a trigger electrode may bepresent. Electrical contacts 114 a, 114 b and 114 c are insertable intoan appropriate measurement device (not shown).

Each of the elongated portions of conductive tracks 112 a, 112 b and 112c can optionally be overlaid with a track 122 a, 122 b and 122 c ofconductive material, such as made of a mixture of silver particles andsilver chloride particles. The enlarged exposed area of track 122 boverlies reference electrode 116. A layer of a hydrophobic electricallyinsulating material 124 further overlies tracks 122 a, 122 b and 122 c.The positions of reference electrode 116, working electrode 118, counterelectrode 120, and electrical contacts 114 a, 114 b and 114 c are notcovered by the layer of hydrophobic electrically insulating material124. This layer of hydrophobic electrically insulating material 124serves to prevent short circuits, and in this embodiment, has an opening126 formed therein. This opening 126 provides the boundary for thereaction zone of biosensor strip 110 and although a rectangular opening126 is illustrated, other shapes may be used (e.g., having arcuate sidesor edges). Because this layer of insulating material is hydrophobic, itcan cause the sample to be restricted to the portions of the electrodesin the reaction zone. Insulating material 124 may be provided in situ,e.g., coated and then cured (e.g., UV cured) or may be applied as asubstrate. The working electrode 118 includes a layer of a non-reactiveelectrically conductive material on which is deposited a layer 128containing a working ink for carrying out an oxidation-reductionreaction.

In FIGS. 5 and 6, the liquid sample flows by means of wicking, typicallychemically aided wicking. Accordingly, biosensor strip 110 of FIGS. 5and 6 contains at least one layer of mesh 130 which overlies theelectrodes. This mesh layer 130 protects the printed components fromphysical damage. Mesh layer 130 also helps the sample to wet theelectrodes by reducing the surface tension of the sample, therebyallowing it to spread evenly over the electrodes. An example of asuitable polyester mesh layer 130 is “Sefar PE-115/36”. A cover 132encloses the surfaces of the electrodes that are not in contact with theelectrode support 111. This cover 132 is a liquid impermeable membrane.

Together, electrode support 111, insulating material 124 (having opening126) and cover 132 define a sample chamber for receiving and holding avolume of liquid sample to be analyzed, the volume being, for example,about 1 microliter or less, e.g., about 0.1-0.3 microliters, or, lessthan about 0.4 microliters. In some embodiments, this sample chamber hasa volume of no more than about 0.3 microliters, e.g., no more than about0.2 microliters, e.g., no more than about 0.1 microliters.

In FIGS. 3 and 4, the liquid sample flows by means of capillaryattraction. Accordingly, in biosensor strip 110′ of FIGS. 3 and 4, alayer of mesh to promote flow of the sample by means of wicking is notpresent.

Biosensor strip 110′ of FIGS. 3 and 4 employs a cover layer 140 and aspacer layer 142, e.g., a layer of adhesive, between electrode support111 and cover layer 140. The adhesive can be a pressure-sensitiveadhesive. The cover layer 140 does not have an aperture. The spacerlayer 142 has a slot 144 that provides the boundary of the reactionzone. Together, electrode support 111, spacer layer 142 (having slot144) and cover layer 140 define a sample chamber for receiving andholding a volume of liquid sample to be analyzed, the volume being, forexample, about 1 microliter or less. In some embodiments, this samplechamber has a volume of no more than about 0.3 microliters, e.g., nomore than about 0.2 microliters, e.g., no more than about 0.1microliters. The liquid sample enters the sample chamber of biosensorstrip 110′ via an opening 146 formed at one end of slot 144 at one endof biosensor strip 110′. The liquid sample is introduced at opening 146and reaches and traverses the reaction zone by means of the action ofcapillary force. Opening 146 can be referred to as an inlet into thesample chamber. The sample chamber is bounded by the sample applicationzone at the proximate end of the biosensor strip, the vent at or nearthe distal end of the biosensor strip, and the edges of the layer ofmesh of a biosensor sensor strip that fills by means of a wicking actionor the edges of the spacer layer of a biosensor strip that fills bymeans of capillary attraction.

Details of the components 111 through 146, inclusive, of the biosensorstrips shown in FIGS. 3, 4, 5 and 6 are described in U.S. Pat. No.6,863,800, incorporated herein by reference. It should be noted thatsubstitutes for the components described in U.S. Pat. No. 6,863,800 arewell known to those of ordinary skill in the art.

In the embodiments of FIGS. 3, 4, 5 and 6, vents can be formed byinserting, between cover 132 and matrix of mesh layer 130 and insulatinglayer 124 of the biosensor strip (or spacer layer 142 only in the caseof a biosensor strip that has dispensed with the mesh layer), anincompressible element 150 into at least one side of the sample chamberor in the distal end (e.g., inlet end) of the sample chamber. Thisincompressible element 150 can be provided in various forms, such as,for example, a thread, a ribbon, a filament, a tape. Incompressibleelement 150 can alternately be, for example, a plurality of threads, aplurality of ribbons, a plurality of filaments, a plurality of tapes.Incompressible element 150 can be constructed of a substantiallyhydrophobic material in order to resist the flow of the sample, whichtypically uses an aqueous carrier. The dimensions of the incompressibleelement 150 are specified by the size and shape of the vent openingdesired. The shape of the cross-section of incompressible element 150can be circular, elliptical, polygonal, typically regular polygonal, orirregular.

Materials that are suitable for preparing incompressible element 150,include, but are not limited to, a multifilament material, such as, forexample, an untreated, braided polyester thread used to manufacturesutures. Such a material is commercially available from PearsallsLimited (United Kingdom) and having the part number 35A103000. Thismaterial is known as EP1 or US size 5/0. The diameter of this materialranges from 0.100 to 0.149 mm. Another material suitable for use in thisdisclosure is a monofilament material typically used as fishing line,commercially available as “WBClarke Match Team”—diameter 0.08 mm 0.80kg, commercially available from sporting goods stores in the UnitedKingdom. Another suitable material is a ribbon having the trademark“DUPONT” “MELINEX”, typically 50 micrometers thick, slit to a width of 2mm and wound on a bobbin.

The incompressible element 150 should be able to resist being deformedby the methods described herein for preparing the biosensor strips. Theincompressible element 150 should also be able to resist being deformedunder normal conditions of storage and use. A “crush” parameter can beused to quantify the desired resistance to deformation. The “crush”parameter takes into account features for preparing the biosensor stripof this disclosure. The “crush” parameter involves and is equal to theseparation between the hot wheel and the support roll or bed plate ofthe hot wheel method, which is described later. The compression that thesilicone rubber coating on the hot wheel experiences as a result of“crush” generates the pressure. The “crush” parameter can be set at aninitial value slightly less than that of the desired product at 0.6 mmand worked down from there to 0.3 mm. A card for forming the biosensorstrip has a typical thickness of 500 micrometers, the layer of mesh hasa typical thickness of 130 micrometers, the backing has typicalthickness of 50 micrometers, and the adhesive has a typical thickness of25 micrometers. The rollers are typically set, via experimentation, at0.45 mm±0.05 mm. One of ordinary skill in the art can set theaforementioned separation of the components of the apparatus properlywithout resorting to undue experimentation.

The step 152 (FIGS. 4 and 6) formed at the interface of the surface ofthe matrix of mesh layer 130 and insulating layer 124 (or spacer layer142 only in the case of a biosensor strip that has dispensed with themesh layer) and the surface of the incompressible element facing thematrix would be positioned upstream of the distal end of the samplechamber or at the distal end of the sample chamber. The step 152 formsan opening that functions as a vent, which would allow the bleeding ofair from either side or both sides of the sample chamber or from thedistal end of the sample chamber. This type of vent has been shown to berobust even when the forces employed in applying the cover to theremaining components of the biosensor strip are high. The vent is easilyverifiable and highly reliable.

When an incompressible element 150 is used to form a vent, the tape thatforms the cover is not as flat as when an incompressible element 150 isnot used, because the majority of the force required to apply the coveris directed through step 152 rather than above the sample chamber, wherethe force is needed to provide a lower profile. This problem does notarise when the vent is created by the use of a plurality ofpressure-sensitive adhesive (PSA) tapes, wherein the firstpressure-sensitive adhesive tape is placed to cover the majority of thesample chamber, but leaves the proximal end, i.e., the fill end, and thedistal end of the sample chamber exposed, and the secondpressure-sensitive adhesive tape covers much of the remainder of thebiosensor strip. The step 152 formed by the incompressible element,i.e., the first pressure-sensitive adhesive tape, leaves two vents inthe sides of the sample chamber. However, the application of a pluralityof tapes increases the amount of pressure-sensitive adhesive tape to becut and, thus, this embodiment is more costly. The application ofthreads, ribbons, filaments, or other incompressible element is oftendesirable on account of simplicity and low cost of materials.

In another embodiment, an ultraviolet-radiation curable (UV-curable)adhesive can be used to form the incompressible element. In thisembodiment, the cover includes a backing having an ultraviolet-radiationcurable pressure-sensitive adhesive on one major surface thereof. Thisadhesive acts as an ordinary pressure-sensitive adhesive initially, butwhen exposed to ultraviolet radiation, it crosslinks and hardens. Inpractice, a narrow deposit of UV-curable adhesive, e.g., about two (2)mm wide, on the backing can be exposed to ultraviolet radiation prior toapplication of the tape to a row containing a plurality of uncompletedbiosensor strips. The narrow deposit of UV-curable adhesive can bepositioned in such a manner that when applied, it will coincide with thedistal end of the sample chamber. In this manner, the narrow depositwould not adhere to the electrodes in the electrode arrangement of thebiosensor strip and the pre-cured adhesive would not flow into thematrix of mesh layer 130 and insulating layer 124 (or spacer layer 142only in the case of a biosensor strip that has dispensed with the meshlayer), thereby ensuring that a vent is formed. The portion of theadhesive layer that has not been exposed to ultraviolet radiation willadhere to the remaining components of the uncompleted biosensor stripvia the aforementioned matrix, when a mesh layer is used, or the spacerlayer, when a mesh layer is not used. After the tape is applied to theremaining components of the biosensor strip, the tape can be exposed toUV-radiation to harden it, thereby reducing the gumming of the cuttingmachines, or allowed to remain uncured and function as a conventionalpressure-sensitive adhesive. The narrow deposit of UV-curedpressure-sensitive adhesive is not adhered to the matrix of the layer ofmesh 130 and insulating layer 124 (or to spacer layer 142 when a layerof mesh is not used), thereby providing vents in the sides of the samplechamber.

The air gap provided by the vent would then be defined by the peaks inthe matrix of mesh layer 130 and insulating layer 124 that separate thecover from the sample chamber or by the unsealed portion at theinterface of the UV-cured pressure-sensitive adhesive and spacer layer142 when a layer of mesh is not used. Easily manufactured vents that arevirtually invisible can be formed in this manner. Ultraviolet-radiationcuring of PSA tapes is compatible with subsequent singulation andpackaging operations.

As still another alternative, the geometry of the layer of insulatingmaterial can be modified to leave a channel exiting from the distal endof the sample chamber, under the cover. This modification is relativelysimple and does not incur additional cost for material. However,modification of the tape application equipment may be required.

Biosensors 110, 110′ of FIGS. 3 and 5 are particularly suited for fastanalyte concentration determination. Many times, the analyteconcentration is determined within 1-10 seconds (e.g., 5-10 seconds)after filling the sample chamber with liquid sample (e.g., blood) to beanalyzed. In some embodiments, the time to determine analyteconcentration is less than 5 seconds (e.g., 3-5 seconds) or less than 3seconds (e.g., 1-3 seconds).

FIGS. 7 and 8 illustrate a biosensor strip having vents in the cover ofthe biosensor strip. In FIGS. 7 and 8, a biosensor strip 210 or 210′includes an electrode support 211, e.g., an elongated strip of polymericmaterial (e.g., polyvinyl chloride, polycarbonate, polyester, or thelike) that supports three tracks 212 a, 212 b and 212 c of electricallyconductive ink, such as carbon (e.g., carbon particles). One suitablesource for conductive carbon ink is Asbury Carbons of Asbury, N.J.Depending on the ink used, it may be combined with other materials tofacilitate processing. These tracks 212 a, 212 b and 212 c determine thepositions of electrical contacts 214 a, 214 b and 214 c, a referenceelectrode 216, a working electrode 218, and a counter electrode 220.Although not illustrated, a trigger electrode may be present. Theelectrical contacts 214 a, 214 b and 214 c are insertable into anappropriate measurement device (not shown).

Each of the elongated portions of conductive tracks 212 a, 212 b and 212c can optionally be overlaid with a track 222 a, 222 b and 222 c ofconductive material, such as a mixture comprising silver particles andsilver chloride particles. The enlarged exposed area of track 222 boverlies reference electrode 216. A layer of a hydrophobic electricallyinsulating material 224 further overlies tracks 222 a, 222 b and 222 c.The positions of reference electrode 216, working electrode 218, counterelectrode 220, and electrical contacts 214 a, 214 b and 214 c are notcovered by the layer of hydrophobic electrically insulating material224. This layer of hydrophobic electrically insulating material 224serves to prevent short circuits. Insulating material 224 may beprovided in situ, e.g., coated and then cured (e.g., UV cured) or may beapplied as a substrate.

In FIG. 8, the layer of hydrophobic electrically insulating material 224has an opening 226 formed therein. This opening 226 provides theboundary for the reaction zone of biosensor strip 210, and although arectangular opening 226 is illustrated, other shapes may be used (e.g.,having arcuate sides or edges). Because this layer of insulatingmaterial 224 is hydrophobic, it can cause the sample to be restricted tothe portions of the electrodes in the reaction zone. For biosensor 210,electrode support 211, insulating material 224 (having opening 226) andcover 232 define a sample chamber for receiving and holding a volume ofliquid sample to be analyzed, the volume being about 1 microliter orless, for example, about 0.1-0.3 microliters, or, less than about 0.4microliters. In some embodiments, this sample chamber has a volume of nomore than about 0.3 microliters, e.g., no more than about 0.2microliters, e.g., no more than about 0.1 microliters.

The working electrode 218 includes a layer of a non-reactiveelectrically conductive material on which is deposited a layer 228containing a working ink for carrying out an oxidation-reductionreaction. In FIG. 8, the liquid sample flows by means of wicking,typically chemically aided wicking. Accordingly, biosensor strip 210contains at least one layer of mesh 230. The at least one layer of mesh230 overlies the electrodes. This mesh layer 230 protects the printedcomponents from physical damage. Mesh layer 230 also helps the sample towet the electrodes by reducing the surface tension of the sample,thereby allowing it to spread evenly over the electrodes. An example ofa suitable polyester mesh layer 230 is “Sefar PE-115/36”. A cover 232encloses the surfaces of the electrodes that are not in contact with theelectrode support 211. This cover 232 is a liquid impermeable membrane.

In FIG. 7, the liquid sample flows by means of capillary attraction.Accordingly, a layer of mesh to promote flow of the sample by means ofwicking is not present. Biosensor strip 210′ of FIG. 7 employs a coverlayer 240 and a spacer layer 242, e.g., a layer of adhesive, betweenelectrode support 211 and cover layer 240. The adhesive can be apressure-sensitive adhesive. The cover layer 240 does not have anaperture. The spacer layer 242 has a slot 244 that provides the boundaryof the reaction zone. For biosensor 210′, electrode support 211, spacerlayer 242 (having slot 244) and cover layer 240 define a sample chamberfor receiving and holding a volume of liquid sample to be analyzed, thevolume being less than about 1 microliter, for example, about 0.1-0.3microliters. In some embodiments, this sample chamber has a volume of nomore than about 0.3 microliters, e.g., no more than about 0.2microliters, e.g., no more than about 0.1 microliters.

The liquid sample enters the sample chamber of biosensor strip 210′ viaan opening 246 formed at one end of the slot 244 at one end of biosensorstrip 210′. The liquid sample is introduced at opening 246 (e.g., aninlet) and reaches and traverses the reaction zone by means of theaction of capillary force. The sample chamber is bounded by the sampleapplication zone at the proximate end of the biosensor strip, the ventat or near the distal end of the biosensor strip, and the edges of thelayer of mesh of a biosensor sensor strip that fills by means of awicking action or the edges of the spacer layer of a biosensor stripthat fills by means of capillary attraction.

Details of the components 211 through 246, inclusive, of the biosensorstrips 210, 210′ shown in FIGS. 7 and 8 are described in U.S. Pat. No.6,863,800, incorporated herein by reference. It should be noted thatsubstitutes for the components described in U.S. Pat. No. 6,863,800 arewell known to those of ordinary skill in the art.

Biosensors 210, 210′ of FIGS. 7 and 8 are particularly suited for fastanalyte concentration determination. Many times, the analyteconcentration is determined within 1-10 seconds (e.g., 5-10 seconds)after filling the sample chamber with liquid sample (e.g., blood) to beanalyzed. In some embodiments, the time to determine analyteconcentration is less than 5 seconds (e.g., 3-5 seconds) or less than 3seconds (e.g., 1-3 seconds).

In the embodiments of FIGS. 7 and 8, covers 232, 240 of biosensors 210,210′ have a series of openings 250 formed through and along the entirewidth of the covers 232 and 240, openings 250 separated from one anotherat specified intervals. The openings 250 are positioned so that at leastone opening is in register with the sample chamber. By judiciousspecification of intervals between openings 250, covers 232 and 240 canhave more than one opening in register with the sample chamber.

A number of methods can be used to form openings 250 in the cover,including, but not limited to, methods using rotary tooling,reciprocating pins, or lasers. Rotary tooling methods can be carried outwith standard (unheated) or heated needles. The advantage of heatedneedles is that they produce smooth, profiled openings and actually meltthe material forming the cover. These openings are less likely toreclose than are those produced by some other mechanical methods.Standard needling tools pierce the cover without removing or reformingthe displaced material, and, accordingly, the use of standard needlingtools gives rise to the risk of forming openings that will reclose ifsufficient pressure is applied when adhering the cover to the remainingcomponents of the biosensor strips.

One type of reciprocating pin tool is a modified engraver. Another typeof reciprocating pin tool includes a pin holder driven by a swash plate.The advantage of the engraver is that its stroke can be varied easily.The advantage of the swash plate fixture is that it can provide variableintervals between openings. Both rotary tooling and reciprocating pintooling have been used successfully to produce openings in covers havingan appearance similar to those produced by standard rotary needlingtools, i.e., wherein the displaced material is not removed or reformed.

An effective method for forming openings in the cover involves formingopenings in a tape, from which segments are cut to form covers, by meansof a process that aligns every opening of the tape in such a manner asto provide proper registration of the openings with the sample chamberof the completed biosensor strip. However, such a process hinders thespeed of manufacture. Openings can be formed in tapes at specifiedintervals, whereby at least one opening will be present in the coverabove each sample chamber on even the narrowest sample chamber deemedacceptable. Such an interval could be as small as 0.5 mm. Formingopenings at such intervals eliminates the need for a time-consumingaligning process.

Mechanical methods of creating openings through the tape often have thefollowing drawbacks:

-   -   (1) The speed required for reciprocating pins is too great for        reliable operation of the pins.    -   (2) The reciprocating pins tend to wear out quickly.    -   (3) No material from the tape is removed by the reciprocating        pins; the material is merely displaced. The openings may        reclose.    -   (4) The spiked roller of a rotary tool tends to wear out        quickly.    -   (5) Again, no material from the tape is removed by the spikes,        thereby allowing possible reclosing of the openings.    -   (6) The spikes are thin and, consequently, weak.    -   (7) The spikes have difficulty in creating the required closely        spaced openings, e.g., intervals between openings of about 0.5        mm.

On account of the foregoing drawbacks, it is often preferred to use alaser to form small openings in the tapes for subsequent formation ofthe covers of biosensor strips. The openings can have a variety ofgeometrical shapes, e.g., circles and dashed lines. Lasers can providegood openings, both from the standpoint of appearance andreproducibility.

A typical laser, e.g., a “SYNRAD” laser (Model 48-2(S), a 25-wattlaser), commercially available from Synrad, Inc., Mukilteo, Wash. 98275USA, a “UNIVERSAL LASER SYSTEMS” laser (Model M300, a 45-watt laser),commercially available from Universal Laser Systems, Inc., Scottsdale,Ariz., can provide openings in various types of tapes that are suitablefor making covers in biosensor strips suitable for this disclosure.

FIG. 9 shows a prototypical laser apparatus 300, which has a laser andassociated optics 302, a rotating shutter disk 304, a braked tapeoff-wind reel 306, a first guide bobbin 308, a top roller 310, a secondguide bobbin 312, a drive roller set 314, and a tape on-wind reel driventhrough a slipping clutch. In FIG. 9, the tape travels from the reel onthe left to the reel on the right. The speed of the tape is typicallymaintained at a constant rate as the tape is passed under the laser andassociated optics. The laser beam is fired through rotating shutter disk304, which has slots to mask the beam at regular intervals, to bringabout the perforating action desired. The tape speed, shutter speed, andlaser power can be adjusted by one of ordinary skill in the art withoutundue experimentation to provide acceptable perforation.

The “SYNRAD” laser does not require a rotating shutter disk, because itcan be pulsed by a computer DAQ card. The “UNIVERSAL LASER SYSTEMS”laser cannot be pulsed automatically, and, consequently requires arotating shutter disk.

Typical settings for perforation of tapes by means of lasers are setforth below.

TABLE I Setting Range Laser power 70% Pulse width 0.5 ms Tape speed 6 to18 meters per min Frequency 200 to 600 Hz, proportional to tape speedTape position 2 mm ± 0.5 mm from laser headThe foregoing settings can be used to provide openings in tapes havingthe following specifications:

Size of opening (approximate diameter) 0.15 mm Interval between openings 0.5 mm

The size of the opening is ultimately dictated by the size of the beamof the laser at the point where the beam converges after passing throughthe lens, i.e., at the focal point. As the tape is moved away from thefocal point, the beam widens, and, consequently, loses ability to burnopenings in the tape. A larger opening can be obtained when the tape ismoved away from the focal point, but there is a point at which the lasercan no longer perforate the tape. Another method of increasing the sizeof the opening would be to utilize a galvo head, which is an arrangementof mirrors that guides the beam of the laser to cut shapes in amaterial. One drawback of the galvo head is that it operates more slowlythan does a single laser pulse. Another drawback of the galvo head isthe failure to remove the solid waste material from the tape. The laserpulse vaporizes the waste material, which is then extracted via anextraction system. The galvo head will leave solids behind, which solidsare likely to stay in the tape or cling to it, the presence of whichwill become evident during subsequent processing steps.

Smaller openings can be obtained by reducing the spot size of the beamof the laser. Moving the focal point further away from the lens createsa more acute angle of approach. Such movement can be used to createsmaller openings. Openings produced by the “SYNRAD” laser are typicallyof a size in the area of 0.15 mm when a 1.5-inch focal length lens isused at a power level of 70% for a 25-watt laser. Settings suitable forlasers for forming openings in tape or other polymeric materials can bedetermined by one of ordinary skill in the art without undueexperimentation.

Various features are affected by (a) the level of power used by thelaser and (b) the duty cycle of the laser. For example, the size of theopenings formed in the tape decreases as laser power drops, everythingelse remaining constant. The size of the openings formed in the tapedecreases as the duty cycle decreases, everything else remainingconstant. Other features are not significantly affected by (a) changesin the level of power used by the laser, (b) the speed of the tape usedin the process of forming openings in the tape, or (c) the duty cycle ofthe laser. For example, the intervals between openings are notsignificantly affected except at very low power levels. As a furtherexample, the intervals between the openings are not significantlyaffected by changes by speed of the tape used in the process of formingopenings in the tape.

A tape, the segments of which are used to form the cover of a biosensorstrip, can be perforated along its entire length with a series ofopenings separated from one another at specified intervals. A typicalopening can have a diameter of about 0.15 mm. A typical interval can beabout 0.5 mm. The position of each opening relative to the elongatededge of the tape is important, but the position of each opening alongthe length of the tape is not. It should be noted that at the time theopenings are formed in the tape, the tape is processed along its length.The entire length of the tape is then applied, e.g., by lamination, to arow containing a plurality of uncompleted biosensor strips, in adirection perpendicular to the direction that the liquid is supposed toflow in the sample chambers. When the completed biosensor strips aresingulated, the perforated tape can provide at least one vent, and insome embodiments a plurality of vents, for each sample chamber.

In an alternative embodiment, a vent can be provided in the cover byusing a narrow tape and leaving a small portion at the distal end of thesample chamber open to the surrounding environment. In other words, thecover resulting from the tape is shorter than the sample chamber. Apractical difficulty with this embodiment involves inaccuracy inapplying the tape and slitting the tape. It is estimated that the distalend of the tape should be placeable to an accuracy of within ±0.2 mm.Modification of the electrode arrangement could reduce the effect ofthis placement problem.

In still another embodiment, the rows from which the electrode supportsof the biosensor strips are formed can be perforated, each row beingperforated along its entire length with a series of openings separatedfrom one another at specified intervals. As with the tape, a typicalopening can have a diameter of about 0.15 mm. A typical interval can beabout 0.5 mm. The position of each opening relative to the elongatededge of the row is important, but the position of each opening along thelength of the row is not. It should be noted that at the time theopenings are formed in the row, the row is processed along its length.The openings are in register with the sample chambers of the electrodesupports of the row. Uncompleted biosensor strips made from the rows canbe overlaid with a tape, the segments of which tape are used to form thecovers of individual biosensor strips. This tape need not be perforated.When the completed biosensor strips having openings in the electrodesupports are singulated, the openings can provide at least one vent, andin some embodiments, a plurality of vents, for each sample chamber.Openings in the rows, or in the cards, if the rows are part of a card,can be formed in the manners described previously for forming openingsin tapes, e.g., by rotary tooling, reciprocating pins, or lasers. Othercomponents of the individual biosensor strips having vents in theelectrode support, e.g., mesh layer, insulating layer, electrodearrangement, can be the same as those described previously forindividual biosensor strips having vents in the cover.

In order to provide a cover for a biosensor strip having a low profile,and further having suitable sample chambers, and still further allowingproduction with minimum changes to current packaging machinery, a tapeincluding a backing bearing an adhesive, e.g., a hot melt adhesive, onat least one major surface thereof can be used. Numerous types ofapplication equipment, e.g., laminating apparatus, can be used. Twotypes of equipment will be described herein.

Referring now to FIG. 10, a prototypical hot wing laminator 400 can beused for preparing biosensor strips that would exhibit a low profile,i.e., minimal dome formation. The hot wing laminator 400 includes atemperature controller (not shown), a shaped heated block 402, a tapereel 404 for paying off tape, a row magazine 406, a feed roller 408 forfeeding rows from the row magazine 406, a set of rollers 410 foradvancing the rows to the station where the tape is laminated to therow, a set 412 of lamination rollers for joining the tape to the row, alamination roller position switch (not shown), pressure regulators (notshown), a tape cutting assembly 414, a feed roller 416 for advancingrows of completed biosensor strips out of the hot wing laminator 400,and a control panel (not shown). In hot wing laminator 400, the tape isheated prior to being laminated and then is applied onto rows ofuncompleted biosensor strips. The process is designed to be continuous.Any tape that has dwelled on heated block 402 will be discarded and notlaminated to uncompleted biosensor strips. The tape dissipates its heatwhen it comes into contact with a row of uncompleted biosensor strips,with the result that a minimum amount of heat is transferred to the rowsof uncompleted and completed biosensor strips.

The hot wing laminator 400 is capable of applying perforated tapeshaving a layer of adhesive adhered to a backing to rows containinguncompleted biosensor strips prior to row conversion. The row magazine406 and feed roller 408 of hot wing laminator 400 can feed rows ofuncompleted biosensor strips from a stack of rows under a set of niprollers 410, which drive the rows through the set of lamination rollers412 of hot wing laminator 400 and define the point where laminationoccurs. After the tape is applied to a row of uncompleted biosensorstrips, the rows are separated by cutting assembly 414, and fed out ofthe apparatus by feed roller 416. The rows have to be cut by cuttingassembly 414 because the tape that forms the covers joins a plurality ofrows. Cutting assemblies suitable for use in this disclosure (i.e., foruse with tapes and tapes having incompressible elements combinedtherewith) and methods for using them are well known to those ofordinary skill in the art. In one type of cutting assembly, used in theprototype, the gap between consecutive rows is sensed by a suitablesensor, and the cutting blade of a pneumatically activated blade carrieris used to cut the tape. A replaceable sacrificial block is used toprolong the life of the blade and ensure a good cut. In the prototypicalapparatus, trimming of the rows is required before the rows can besubjected to any further processing steps. This step can be eliminatedthrough the use of more precise apparatus. Such an apparatus couldcomprise a blade carrier having two cutting blades, an upper stripper,and a lower stripper. The gap between consecutive rows is aligned withthe cutting blades. The cutting blades and upper stripper move down ontothe row (or rows if a card containing a plurality of rows is used). Thecutting blades are slightly inboard of the terminal edges of the rows.Downward pressure is applied by the cutting blades and the upperstripper. The lower stripper advances upwardly and clamps the tapeagainst the upper stripper. The force exerted by the lower stripper isdesigned to be greater than that of the upper stripper, and,consequently, the clamped tape is moved upwardly. The cutting bladesremain stationary, thereby allowing the tape to be cut. The upperstripper is retracted, leaving the waste tape to be removed by vacuumfrom between the blades. The cutting blades and lower stripper areretracted, leaving the two rows separated.

The shaped, heated block 402 activates the hot melt adhesive coated ontothe backing of the tape. The tape is drawn over heated block 402 atminimal tension, and the shape of heated block 402 ensures good contactbetween the tape and heated block 402 over the extent of travel of thetape. The heated block 402 is often referred to as the wing, on accountof its shape.

The hot wing laminator 400 can process rows of uncompleted biosensorstrips and tapes at a speed of 12 meters per minute. Higher or lowerspeeds can be used, if the other parameters of the method are adjustedin a suitable manner. The hot wing laminator 400 can be set to heat thetape up to a temperature of 130° C. Higher temperatures can be used, butare not preferred. The following settings are typical of those that canbe used to carry out the method effectively:

-   -   Wing temperature 120° C. to 130° C.    -   Lamination speed 12 meters per min        In addition to the foregoing settings, hot wing laminator 400        can operate with an air supply of 6 to 8 Bar and an electrical        supply of 240 volts AC. The purpose of the air supply is to        operate the pneumatically driven cutting apparatus. The hot        wheel laminating apparatus can be bench-mounted.

The following description of a detailed procedure applies to a hot winglaminator that can be used to prepare biosensor strips of thisdisclosure. The procedure relates to an apparatus constructed in anengineering laboratory. It is expected that the apparatus will be scaledup for the purposes of commercial production. When scaled-up, it isexpected that the apparatus can apply tapes to cards, in addition toapplying tapes to rows. The temperature controller (not shown) allowsthe cycle only when the temperature of the wing is within 1° C. of thetarget value. When the guard doors (not shown) are opened or theemergency stop (not shown) is operated, the power to the heater (notshown) is lost, so the heater begins to cool down. The power is returnedonly when the emergency stop (not shown) is pulled out, the guard doors(not shown) are shut, and the reset button (not shown) has beenactivated. A minimal amount of time with the guard doors (not shown)open will ensure that laminator 400 is ready for operation. The controlpanel (not shown) contains the buttons referred to in the followingdescription. The steps for applying covers to rows of uncompletedbiosensor strips are set forth below:

-   -   1. Ensure that all the guards (not shown) are closed    -   2. Turn on the air supply at the isolation switch on the back of        the machine (not shown).    -   3. Turn on the electrical supply at the switch (not shown) on        the plug on the wall (not shown).    -   4. Ensure that the emergency stop (not shown) is pulled out.    -   5. The blue reset button (not shown) should flash.    -   6. Press the blue reset button (not shown).    -   7. Turn on the heater switch (not shown) on the far right of the        control panel (not shown). The switch (not shown) will be        illuminated when the heaters are on.    -   8. Wait for hot wing 402 to reach the appropriate temperature.    -   9. Ensure that the rows to be laminated are all in the same        orientation and no edges from the windy miller (not shown) are        present.    -   10. Ensure that there is a sufficient supply of tape to complete        the required number of rows.    -   11. When hot wing 402 reaches the appropriate temperature, open        the guards (not shown) and load the tape onto off-wind spool        404.    -   12. Undo the thumbscrew (not shown) in the center of the spool.    -   13. Remove the friction plate (not shown) and the empty core        (not shown).    -   14. Ensure that the tape on the reel to be loaded has been        perforated.    -   15. Load the tape reel with the adhesive side of the tape facing        upwardly and the perforations to the back of the machine.    -   16. Fit the thumbscrew (not shown) and friction plate (not        shown) to ensure that the reel is as loose as possible without        causing wander.    -   17. Thread the tape under roller 418 and over the first guide        (not shown) on hot wing 402. The hot wing 402 should not be        touched.    -   18. Pull the tape down the length of hot wing 402 and thread        through the slot (not shown) in the bed (not shown) of the        machine.    -   19. Ensure that the tail hanging below the bed (not shown) of        the machine is visible below the roller level.    -   20. After the tape is loaded, fill row magazine 406 with the        rows of uncompleted biosensor strips to be laminated. Orient the        rows so that the sample chamber is to the back of the machine        with the face up.    -   21. Lift the weight (not shown) in row magazine 406 and feed the        rows under the weight. Ensure that the rows are butted up        against the out feed end of row magazine 406 and lower the        weight (not shown) on top of the rows.    -   22. Ensure that the lamination roller position switch (not        shown) is in the down position.    -   23. Close the guards (not shown), ensure that the emergency stop        (not shown) is not operated, and press the reset button (not        shown).    -   24. When the temperature reaches a point within 1° C. of the        target temperature, the rows are loaded, and the air is on, the        green start button (not shown) will flash to indicate that the        machine is ready to laminate the rows.    -   25. Push the green start button (not shown). The motors (not        shown) will start in order from row out feed to row in feed.    -   26. The first row will be fed through the machine and pick up        the tape as it passes the slot (not shown) in the bed (not        shown) of the machine prior to the set of lamination rollers        412. The tape will start to pay out over hot wing 402 and down        into the rows.    -   27. The rows will be separated from each other by cutting device        414 at the end of the bed (not shown).    -   28. The rows will be fed out of the back of the side of the        machine by feed roller 416 and can be collated by hand and        trimmed to enable singulation to take place. The first three        rows from the start of the run should be discarded, as these        will be produced from tape that has been allowed to dwell on hot        wing 402.    -   29. When the rows have run out, the final row will stop at the        end of the bed (not shown), hanging out of the side of the        machine. The motors (not shown) will stop.    -   30. Remove this row by pressing the down button (not shown) on        the control panel (not shown) and pulling the row free of the        machine at the same time.    -   31. Open the guard (not shown) and remove the tape, which has        fed up to cutting device 414. This step is best achieved by        teasing the tape away from wing 402 and cutting, thereby        allowing the tape on the bed (not shown) to be pulled in the        opposite direction to the machine operation. This will ensure        minimal amounts of hot melt adhesive will be transferred to the        bed (not shown) and the rollers of the machine.    -   32. Clean any areas of the bed (not shown) and rollers, which        have deposits of adhesive.    -   33. To process another lot of rows, the machine will have to be        set up following from step 9 of this procedure.

The foregoing method can be scaled up to process cards having aplurality of rows instead of individual rows by modifying the apparatusto render it capable of handling a plurality of reels of tape forforming covers for forming completed biosensor strips.

Samples of uncompleted biosensor strips having components substantiallyas described in U.S. Pat. No. 6,863,800 can be processed on hot winglaminator 400. As indicated previously, hot wing laminator 400 heats theperforated tape, segments of which form the covers, over heated block402 prior to the tape's being adhered to the remaining components of thebiosensor strips on the row by a rubber roller. No heat is applied tothe tape at the point where lamination of the tape to the row occurs,with the result that any heat from the tape is quickly dissipated intothe row.

There are several advantages in using a hot wing laminator and somedisadvantages. The hot wing laminator is capable of working with varioustypes of insulating materials, e.g., “SERICOL” insulating ink(commercially available from Sericol, United Kingdom) and “KROMEX”insulating ink (commercially from Kromex, United Kingdom). The exposureof the tape to hot spots is consistent with this laminator. The hot wingis a good conductor. Slip rings are not required. No heat is transferredfrom the hot wing to the uncompleted biosensor strip at the point oflamination. The hot wing laminator is easy to thread and easy to clean.The hot wing laminator can process tape at a rate of 12 meters perminute, which is considered fast. However, this speed could adverselyaffect tape cutting and row feeding. The hot wing laminator is notreadily adjustable for material tolerance. The surface of the hot wingis susceptible to wear. The tape has to move along the hot wing.

Another type of laminator that can be used to prepare tapes describedherein is a hot wheel laminator, illustrated in FIGS. 11 and 12. The hotwheel laminator 500 can be used to laminate the tape, segments of whichform the covers of the biosensor strips, to the remaining components ofuncompleted biosensor strips printed in rows. Referring now to FIGS. 11and 12, hot wheel laminator 500 includes a tape-dispensing roll 502, aguiding system 504 including a roller, a hot wheel 506, a dispenser 508for the incompressible element, and a guide 510 for guiding theincompressible element dispensed from dispenser 508 to hot wheel 506.Tape is fed from tape-dispensing roll 502, passes through a guidingsystem 504, which urges the tape against the surface of hot wheel 506.The tape is fed around roller 504 and onto hot wheel 506. The hot wheel506 is typically driven at six (6) meters per minute and is kept at aconstant temperature by cartridge heaters and a control circuit. Atemperature that is suitable for the hot wheel roller is 180° C. Higheror lower speeds can be used, if the other parameters of the method areadjusted in a suitable manner. The hot wheel 506 has a silicone rubbersurface, which enables the hot wheel to conform to the row at the pointof lamination. The hot wheel 506 can be driven by a 24 volt DC motor.The voltage supplied to the motor is set to achieve the desired speed.Rows of uncompleted biosensor strips 512 can be fed into the apparatusby hand and separated after the lamination operation. Tape that hasdwelled on hot wheel 506 can be discarded and not used to complete thebiosensor strip. FIGS. 11 and 12 also show a dispenser 508 fordispensing an incompressible element onto the layer of adhesive on thetape when the tape is on hot wheel 506. As the tape is drawn around hotwheel 506, the adhesive side of the tape faces outwardly of hot wheel506. The incompressible element, e.g., a thread in FIGS. 11 and 12, isthen applied into the softened layer of adhesive. The hot wheel 506 thenlaminates the tape containing the incompressible element on the row ofuncompleted biosensor strips 512. On the prototype apparatus, a cuttingassembly (not shown) separates the individual rows, because the tapethat forms the covers joins a plurality of rows. Cutting assembliessuitable for use in this disclosure (i.e., for use with tapes and tapeshaving incompressible elements combined therewith) and methods for usingthem are well known to those of ordinary skill in the art. Such cuttingassemblies have been described previously, in relation to the hot winglaminating apparatus. The cut rows of completed biosensor strips arerepresented by the reference numeral 514.

To prepare rows for feeding into the hot wheel laminating apparatus,electrode arrangements, reagents, and certain other components areprinted onto a web of polyester sheet. The web typically has a patternof six arrays of uncompleted biosensor strips. In the last step of theweb printing process, the web is cut into cards (e.g., 255 mm wide and304 mm long), each containing six rows of 50 uncompleted biosensorstrips per row. Subsequently, layers of mesh and layers of insulatingmaterial are applied to the uncompleted biosensors on the card. Forprototype work, the cards are cut into six rows. The dimension of a rowis, e.g., 304 mm long by 40 mm wide. Each row contains 50 uncompletedbiosensor strips. For commercial operations, the cards need not be cutinto rows prior to application of the tape to the uncompleted biosensorstrips. Rows are easier to handle in prototype work, but in commercialproduction, the tape for forming the cover of the biosensor strip isapplied to the cards prior to converting the cards into rows. When usingcards in commercial production operations, additional dispensers fortape and incompressible elements and additional cutting assemblies canbe used to scale up production. Returning now to the discussion of theprototype, the tape and the incompressible element are applied to therows simultaneously in a continuous manner. The rows of the completedbiosensor strips are then row converted to give rows having dimensionsof, e.g., 304 mm long by 34.5 mm wide. Approximately 5.5 mm of materialis removed from the edge of the row adjacent to the proximal end of thesample chambers. Finally, the converted rows are processed by subjectingthem to a set of blades to singulate the cards into individual biosensorstrips.

The hot wheel laminator improves the positional accuracy of the tape byimproving the location of the rows and improving the tape feed features.The rows are forced up to a datum edge prior to and subsequent tolamination of the tape to the remaining components of the of thebiosensor strips on the rows. This operation is achieved by springrollers, which compensate for variations in the width of the row at theminor surface of the row that contacts a fixed guide. To furtherexplain, if a row, or a card in the case of a scaled-up operation, has awidth tolerance of ±0.2 mm, fixed guides would have to be set for thewidest row (or card). Assuming that a line could be scribed with perfectaccuracy at a given point on the row (or card), if a row (or card)having the lower size limit is fed into the apparatus, the position ofthis scribed line could be anywhere within a band having a width of 0.4mm. One edge of the row (or card) is assigned as the datum edge and thatedge is assigned a corresponding fixed guide. So long as the oppositeedge has spring rollers to compensate the variations in width, the linewill always be scribed in the same position.

The tape is guided up to a datum edge and fed onto the hot wheel 506.The hot wheel lamination method improves the process tolerance bycompensating for variations in the materials undergoing the process. Thehot wheel 506 transfers heat to the tape and melts the hot melt adhesivecoated on the backing of the tape. The hot wheel 506 will remain incontact with the tape until the tape has been laminated to the row ofuncompleted biosensor strips. The method employing hot wheel laminator500 differs from the method employing hot wing laminator 400 in that inthe method employing the hot wheel, the heat is still being applied atthe point of lamination. The hot wheel method, like the hot wing method,is designed to be continuous.

A hot wheel laminator has numerous advantages and some disadvantages.The hot wheel laminator can run at lower speeds than can the hot winglaminator. Cutting of tape is easier at lower speeds. The hot wheellaminator can work with various types of insulating layers, e.g.,“KROMEX” insulating layer and “SERICOL” blue insulating layer. The hotwheel 506 rotates with the tape, with the result that the tape will notbe scratched or smeared. Direct heating improves the bond strengthbecause the tape does not begin to cool until after lamination; however,heat applied directly to a row or card brings about the risk of slightlydenaturing the enzyme. Furthermore, the wheel has to be coated withrubber, e.g., silicone rubber, and rubber is a poor conductor of heat.The temperature setting of hot wheel is 50° C. higher than that of thehot wing laminator. Hot spots on wheel, which are caused by spaced apartheating elements, expose specific sections of tape to highertemperatures. In contrast, in the hot wing laminator, hot spots on thewing, which are also caused by spaced apart heating elements, expose allsections of the tape to higher temperatures. The wheel may be difficultto thread. Slip rings are required for heaters and thermocouples.

While the foregoing methods relate to applying tapes having a backingbearing a layer of hot melt adhesive, it is also within the scope ofthis disclosure to use tapes having a backing bearing apressure-sensitive adhesive to form the covers of biosensor strips. Thehot wheel laminator and the hot wing laminator would not be used withtapes having layers of pressure-sensitive adhesive. A laminatingapparatus equipped with pressure rollers can be used to apply a tapehaving a backing having a layer of pressure-sensitive adhesive to theuncompleted biosensor strips. The steps subsequent to applying the tapeto the uncompleted biosensor strips would be substantially similar tothose steps carried out subsequent to applying a tape employing a hotmelt adhesive to uncompleted biosensor strips.

The following non-limiting examples further illustrate various aspectsof this disclosure. In the following examples, it should be noted thatthe specific electrodes and their positions in the electrodearrangements are not specified, not are the reagents applied to theelectrodes, if any specified. For the purposes of this disclosure, suchdetails are not relevant. Appropriate placement of electrodes in anelectrodes arrangements and appropriate selection of reagents are wellknown to those of ordinary skill in the art, without undueexperimentation.

EXAMPLES Example 1

This example illustrated settings for the hot wing apparatus forlaminating the cover layer to the remaining layers of a biosensor stripto achieve good adhesion after cutting without the need for coronatreatment.

Cards having an electrode support, an electrode arrangement, and a layerof mesh were prepared on a print line and then cut into rows on thewindy miller row cutter. Two insulating layers from Sericol were tested:one was lilac (“SERICOL” light blue, LDA 25) and the other green(MediSense part number B03010).

The hot wing laminator was set at a temperature of 90° C. and 10 voltsfor the motor speed. There is a substantially direct correlation ofspeed as a function of voltage, with 18 volts being approximately equalto a tape speed of 21 meters/minute.

A stack of five (5) rows was prepared for feeding through the apparatus:two scrap rows to consume the tape that had dwelled on the hot wing,then the rows employing (a) the lilac insulating layer and (b) the greeninsulating layer, and finally another scrap row at the bottom of thestack to force the two sample rows out of the hot wing laminator. Thetwo sample rows were separated from the scrap rows and trimmed to ensurethat the tape for forming the covers of the biosensor strips was flushwith the sides of the row. The two rows were then cut on a cuttingmachine and potted. The pots were marked for later identification.

The apparatus was set from 10 volts to 20 volts in increments of 2volts, and the temperature of the hot wing was set from 90° C. to 130°C. in increments of 10° C., with one lilac sample and one green samplebeing produced and singulated on a cutting machine at each setting.Testing was conducted in two parts. The first part involved a visualinspection of the tape on the biosensor strip to establish whether ornot the tape was bonded after the cutting. When the tape delaminatesfrom the remaining components of the biosensor strip, light patches canbe seen between the cover and the matrix of the mesh layer and theinsulating layer. When the tape remains bonded to the remainingcomponents of the biosensor strip, the adhesive interface appears to bedark and wetted. The second test involved a hand-operated test, in whichthe biosensor strip was held at each end, and the first end was twistedclockwise and the second end was twisted counterclockwise, at a totalangle of 90° to stress the adhesive. Then, the second end of thebiosensor strip was then twisted counterclockwise and the first endtwisted clockwise, at a total angle of 90° to further stress theadhesive. Any delamination was not acceptable.

At the 90° C. level, all samples delaminated after the 90°/90° twisttest. At the 100° C. level, none of the green samples passed the 90°/90°twist test. The cutting machine stressed the strips as they weresingulated, causing the cover to delaminate from the remaining layers. Asimilar, but less pronounced, effect occurred with the lilac strips inthe 90°/90° twist test. At the 110° C. level, none of the green samplespassed the 90°/90° twist test. The lilac strips showed better adhesionto the remaining layers of the biosensor strip in the 90°/90° twisttest, but still exhibited some delamination. At the 120° C. level, thebonds formed with the green strips showed some improvement in the90°/90° twist test. The lilac strips showed some delamination in the90°/90° twist test at low to moderate speeds (e.g., 14 volts), but nodelamination at higher speeds (e.g., 16-20 volts). At the 130° C. level,all of the green strips delaminated in the 90°/90° twist test, but lessdelamination occurred at higher speeds. The lilac strips performed wellat all levels, with no delamination exhibited after the 90°/90° twisttest. The 90°/90° twist test proved that the adhesive was still bondedafter the singulation process and could take some abuse. Based on thesetests, it was determined that the optimum settings for the hot winglaminator were from about 120° C. to about 130° C. and a tape speed thatcorrelates with a voltage of 16-20 volts.

Example 2

The purpose of this example was to establish an average minimum andmaximum figure for the displacement of hot melt adhesive into the weaveof surfactant coated mesh (FC 170 surfactant, PE 130 mesh) during thelamination process employing the hot wing laminator.

When tape is removed from a row to which the tape has bonded well, theadhesive that has bonded to the insulating layer remains on theinsulating layer and separates from the backing. The area of theadhesive that overlies the sample chamber, i.e., the area of the meshthat has no insulating layer, remains on the backing that has beenremoved and the imprint of the mesh can be seen in the adhesiveremaining on the backing. The imprint remaining in the adhesive on thebacking indicates that displacement of adhesive into the mesh hasoccurred.

Samples were processed on the hot wing laminator. The insulating layerwas “KROMEX” insulating layer. The hot wing laminator heated the tape(MediSense part number R11003) over the hot wing prior to lamination,which was performed by a rubber roller. No heat was applied to the tapeat the point of lamination, so any heat was quickly dispersed into therow. The settings used were a wing temperature of 130° C. and a tapespeed of 12 meters per minute.

Once the tape had been laminated to the remaining components of thebiosensor strip, the samples were allowed to stand for one day. The tapewas then peeled from the biosensor strips by hand and a short sectionwas cut for scanning via a “PROSCAN” profilometer and examination on ascanning electron microscope (SEM).

When a transparent sample is scanned (i.e., the adhesive used in thisexample is transparent), the light does not reflect as well as it wouldreflect from an opaque, colored surface. To overcome this problem, acolored material, e.g., gold, has to be sputtered onto samples of meshprints in hot melt adhesive prior to examination. The colored surfacecan be read better by the profilometer than can the surface of atransparent adhesive.

The scanned image was evaluated by using “PROSCAN” software suppliedwith the “PROSCAN” profilometer. A selected cross section of the surfaceshowed six (6) of the mesh strand impressions from a given strand,running across the length of the mesh. The section tool in the softwarerecorded the peaks and troughs of the weave. The lowest point in thetrough was subtracted from the height of the peak on the left side ofthe trough and then subtracted from the height of the peak on the rightside of the trough. The average of these 12 results was calculated togive the amount that the mesh had sunk into the molten adhesive. Thefollowing table shows the results of these determinations. Dimensions inthe table are in micrometers.

TABLE II Left Right Lowest Left Right side side point in side sideRecess peak peak trough depth depth 1 197.28 193.23 159.21 38.07 34.02 2208.17 205.73 162.22 45.95 43.51 3 208.72 209.47 165.94 42.78 43.53 4213.69 210.04 169.64 44.05 40.4 5 214.32 203.65 165.81 48.51 37.84 6209.17 207.07 170.44 38.73 36.63 Maximum 48.51 Minimum 34.02 Average41.17The average amount of hot melt adhesive intrusion into the mesh wasapproximately 41 micrometers. The weave was clearly visible fromphotographs (not included) and the profilometer scan (not included).

Example 3

The purpose of this example was to identify the cause of the increase intension experienced with the hot wing laminator. Increased tension onthe tape from which the cover is formed results in bowing of the rowsfrom which the biosensors are formed. Increased tension could also causethe row drive system to fail, the tape positional accuracy to wander,and the tape for forming the cover to stretch.

Openings were formed in the tape by means of a prototype laserapparatus. The speed of the tape was maintained at a constant rate asthe tape passed under the laser. The tape handling components wereplaced under the Universal Laser Systems profile-cutting laser, and thelaser beam was fired through the through the rotating shutter disk 304,which has slots to mask the beam at regular intervals, to bring aboutthe perforating action desired.

Initial tapes formed were laminated to rows on the hot wing laminatorwith no detrimental effect. The tapes used were 20.5 mm wide by 325meters long to scale up the method. The tape was loaded with theadhesive layer facing outwardly of the core of the roll. Previously, theadhesive layer faced inwardly to the core of the roll.

The rows produced from the first roll of perforated tape for preparingthe covers of the biosensor strips exhibited excessive bowing. Bowedrows are an indication of high tension in the tape during the laminationprocess. Bowed rows are not acceptable for subsequent downstreamprocesses and handling operations. It should be noted that bowed cardsare not acceptable for downstream processes and handling operations incommercial production operations. Possible causes for the high tensionwere identified:

(1) In scaling up the manufacturing of low-profile biosensor strips, thediameter of the roll of tape is increased to accommodate more rows perperforated roll. Tension control is achieved by applying pressure to thecore of the roll of tape to cause friction. As the roll decreases indiameter when the tape pays off, the tension increases because theleverage about the center of the roll decreases. The best results fromthe laminators have been achieved with the lowest amount of tension onthe tape as possible.(2) When mistakes are made in loading the tape onto the wing, i.e.,adhesive side in contact with the surface of the wing, adhesive betweenthe wing and the backing causes the tape to drag over the surface of thewing and increases the tension.(3) If adhesive transfers onto the side of the tape that is in contactwith the hot wing, the adhesive is softened, thereby causing the processto bind up in a fashion similar to that in which the adhesive adheres tothe wing. Adhesive could be deposited onto the backing of the tapeduring the laser perforation process.

The following tests were performed to determine which of the foregoingpossibilities caused of the increased tension in the tape. The wing wascleaned between each test.

Test 1 (Roll Diameter)

Two rolls of unperforated tape were processed on the hot wing laminator.One roll had a large diameter, and the other roll had a small diameter.No difference was observed between the two batches of products produced.Accordingly, roll diameter was discarded as a cause for the increasedtension.

Test 2

One perforated roll of tape and one unperforated roll of tape, each rollhaving the same diameter, were processed in turn on the hot winglaminator. The rows produced with the perforated roll showed the signsof the high tension in the tape. The rows produced with the unperforatedroll showed no sign of bowing.

This result pointed to an effect caused by the perforation of the tape.Upon closer inspection, it was noted that the roll of perforated tapehad been perforated from the adhesive side of the tape. Previously runtapes, which had been perforated from the backing side of the tape, didnot show this effect. This change in perforation direction was directlylinked with the change in roll format. Previously, the adhesive layerfaced inwardly to the core of the roll.

Test 3 (Perforation Direction)

Two rolls of perforated tapes were produced with the same settings onthe laser apparatus. The first roll was perforated from the backing sideof the tape. The second roll was perforated from the adhesive side ofthe tape. Both rolls were of the same diameter.

Both rolls were processed to make covers on uncompleted biosensor stripson rows on the hot wing laminator. The tape perforated from the adhesiveside resulted in rows of completed biosensor strips that exhibitedbowing, while the tape perforated from the backing side resulted in rowsof completed biosensor strips that still showed slight bowing, but farless than did the rows of completed biosensor strips prepared from tapeperforated from the adhesive side.

There were a number of possible reasons why the tape binds to the hotwing laminator when perforated from the adhesive side of the tape, i.e.,wherein the adhesive layer is between the laser and the backing of thetape.

(1) The prototypical laser utilized extraction from the Universal LaserSystem unit, which was not specifically designed to extract in the areawhere the holes were formed, with the result that the vapor expelledfrom the tape during the process was free to reattach itself to thetape.(2) The laser lens had a positive pressure of clean air applied to it.Clean air keeps the lens free from airborne contaminants during theprocesses for forming openings in the tape. This positive pressure couldforce the vaporized adhesive through the opening to be deposited on thebacking side of the tape. When perforated from the backing side of thetape (i.e., when the backing is between the laser and the adhesivelayer), the positive pressure prevents the adhesive from reaching thebacking side of the tape.(3) Every time the reel is changed, the roller directly below the pointwhere the opening is formed is cleaned, because deposits from theopening-forming process tend to build up in this area. Also, depositsfrom the opening-forming process build up on the nip rollers, which drawthe tape at the constant speed. When the tape is perforated from theadhesive side of the tape, the upper nip roller collects the deposits.When the tape is perforated from the backing side of the tape, the lowernip roller collects the deposits but at a far lower rate.

When the tape is perforated from the adhesive side, the tape binds onthe hot wing. Tapes to be applied by the hot wing laminator can beperforated from the backing side to ensure that rows produced areacceptable.

Example 4

The purpose of this example was to establish process settings for thehot wheel laminator.

Cards (polyester) having an electrode support, an electrode arrangement,and a layer of mesh were prepared on a print line and then cut into rowson the windy miller row cutter. The insulating materials were “SERICOL”light blue (lilac) (part number LDA 25) and “KROMEX” blue (part numberMediSense Blue 56847).

The temperature of the hot wheel laminator was set from 200° C. to 150°C. in steps of 10° C. with four samples having a “SERICOL” insulatinglayer and four samples having a “KROMEX” insulating layer being producedand then singulated on the cutting machine at each temperature level.

The hot wheel laminator was set at a temperature of 200° C. and allowedto stabilize for 10 minutes. After the stabilization period, the gapbetween the upper roller 506 and the lower roller (not shown) waschecked with a feeler gauge and adjusted to 0.6 mm. A stack of 11 rowswas prepared for feeding through the apparatus: (a) two scrap rows toconsume the tape that had dwelled on the hot wheel apparatus; (b) thenfour sample rows of “SERICOL” insulated uncompleted biosensor strips;(c) then four sample rows of “KROMEX” insulated uncompleted biosensorstrips, (d) finally another scrap row at the bottom of the stack toforce the sample rows out of the hot wing laminator. The two sets ofsample rows were separated from the scrap rows and trimmed to ensurethat the tape was flush with the sides of the row. The samples were thengiven identifying split numbers and row-converted on a hand-operated jigon the print line. The samples were then singulated in isolated splitson the cutting machine. Samples were bagged and identified forsubsequent testing.

The temperature of the hot wheel laminator was set at 190° C. andallowed to cool. The gap was checked and adjusted to 0.6 mm and anothereight samples were produced in the manner described above. The foregoingmethod of preparing samples for testing was carried out at 180° C., 170°C., 160° C. and 150° C., eight samples being prepared at eachtemperature in the manner described previously.

Testing was carried out in three parts. The first part involved a visualinspection of the tape on the strip to establish whether or not thecover was bonded after the cutting. When the cover delaminates from theremaining components of the biosensor strip, light patches could beseen. When the cover remains bonded to the remaining components of thebiosensor strip, the appearance of the tape was dark.

The second test employed a hand-operated device, which gripped the stripat each end and twisted the ends in opposite directions to stress theadhesive. Three cycles of the twist were completed and the strip removedfrom the twisting device. Any delamination was not acceptable. Tosimplify evaluation of the delamination, a red colored control solutionwas added to the biosensor strips. The control solution wicked into theareas of delamination around the sample chamber. Any solution outside ofthe sample chamber indicated that the strip was not acceptable.

The third test was in response to inconclusive results obtained from thetwist test.

No delamination was observed with any of the samples. All of the samplestested were compatible with the cutting machine. However, when sampleswere peeled by hand, it seemed that the strength of the bond increasedas temperature of bonding increased. However, exposure to heat may, inthe long run, delaminate the rubber coating from the wheel, which ismade of steel and/or aluminum.

Example 5

The purpose of this example was to establish tolerances for the methodof preparing samples by means of the hot wheel laminating apparatus. Theapparatus was a prototype.

The rows used for the study were finished up to and including the stepsof applying the mesh layer and insulating layer. The rows were processedwith the hot wheel at a temperature of 150° C. The samples were fedthrough the laminator, collected, and evaluated.

A “Mitutoyo Quick Vision PRO” analyzer was used to measure the distanceparameters of the samples. The position of the tape from the datum edgewas measured at three points on each row. The three points were atbiosensor strip 1, biosensor strip 25 and biosensor strip 50. FIG. 14shows the biosensor strips in a given row. A cell is synonymous with anuncompleted biosensor strip. Ten rows were evaluated. The results werecollated and processed to establish the variances in positioning. Theminimum measurement was subtracted from the maximum measurement for eachrow to give the variation in position of each row. The minimum value ofthe entire set of 30 measurements was subtracted from the maximum valueof the entire set of 30 measurements to provide overall variance of thetape application process. The allowable range between the maximum andthe minimum is 0.2 mm. The hot wheel apparatus can apply tape within avariance range of 0.15 mm, so it was concluded that a tolerance of 0.1mm would be achievable. TABLE III summarizes the results of the 30measurements.

TABLE III Biosensor Biosensor Biosensor strip 1 strip 25 strip 50Overall Maximum (mm) 5.87817 5.85649 5.86155 5.87817 Minimum (mm)5.76053 5.7329 5.74081 5.7329 Range (mm) 0.11764 0.12359 0.12074 0.14527Average of 10 5.822578 5.812224 5.796312 5.810371 measurements (mm)

Example 6

The purpose of this example was to show the effectiveness of laserperforation of tapes for preparing covers for the biosensor strips. Allsamples were produced using the following equipment:

“IDENT” tape slitting machine

Tape rewind fixture

“SYNRAD” 25 watt laser

Computer with NI DAQ card

All measurements were taken a “Mitutoyo Quick Vision PRO” analyzer.

The equipment was set up to account for the following variables:

Laser power

Tape speed

Operation signal frequency

Duty cycle

Tape distance from laser aperture

Two types of tape were used for testing:

(1) Green polyester tape coated with hot melt adhesive in current use;

(2) The blue UV-curable PSA tape supplied by Adhesives Research,Ireland.

The blue tape was used to ensure that the maximum foreseeable thicknessof 130 micrometers could be perforated by the laser. Tapes were slit toa width of 15 mm on the Ident slitting machine and rewound. The tapeswere then used for the following tests.

Test 1

Blue Tape: UV Opening Size as a Function of Laser Power at Tape Speed 6Meters Per Minute

This test was used to establish the optimum laser power setting forproducing an opening at a tape speed of 6 meters per minute. This speedwas suggested, as it equates to the target cycle time of 3 seconds. Thespeed of the tape was set to 6 meters per minute, and the laser wasfired at 180 Hz. These settings were expected to provide intervalsbetween openings of 0.55 mm. The laser power was decreased in incrementsof 10% between splits from 95% to the point at which no measurementcould be taken with the “Mitutoyo Quick Vision PRO” analyzer.

Test 2

Blue Tape: UV Opening Size as a Function of Laser Power at 18.5 MetersPer Minute

This test was used to establish the optimum laser power setting forproducing an opening at a tape speed of 18.5 meters per minute. Thisspeed was suggested, as it is the maximum speed of the test apparatus.The frequency was 624 Hz. These settings were expected to provideintervals between openings of 0.494 mm. The laser power was decreased inincrements of 10% between splits from 95% to the point at which nomeasurement could be taken with the “Mitutoyo Quick Vision PRO”analyzer.

Test 3

Green Tape: Opening Size as a Function of Duty Cycle at 6 Meters PerMinute

This test was used to identify the effect of duty cycle on the size ofthe opening obtained. The tape speed was set to 6 meters per minute. Thelaser was set at 95% power, and the duty cycle was reduced from 18% invarious steps until no opening could be measured. The duty cycle is thepercentage of the cycle time that the laser is actually firing.

Test 4

Green Tape: Opening Size as a Function of Duty Cycle at 18 Meters PerMinute

The settings were the same as in Test 3, but the rate of speed of thetape was set at 18 meters per minute with corresponding frequency andduty cycles calculated to yield the same pulse width for each stage ofthe test, i.e., starting at 0.5 ms, which is 31% of a frequency of 624Hz. It is important to point out that pulse width has more meaning tothese runs than does duty cycle. The higher the frequency for the sameduty cycle, the shorter the pulse width becomes. As the duration of thepulse width decreases, the time that the laser has to burn the openingsdecreases.

Test 5

Green Tape: Opening Size and Intervals Between Openings for VariousSpeeds at 0.5 Ms Pulse Width

The laser power was set to 70%. The duty cycle was calculated for eachtape speed and laser frequency to give a pulse width of 0.5 ms. The tapespeeds varied from 18 meters per minute to 6 meters per minute in 1meter per minute increments.

Test 6

Green Tape: Usable Focal Length of Laser

A focal length test was used to determine to what extent the distance ofthe tape from the aperture of the laser could vary during production ofopenings in the tape. The tape rewind fixture was fitted to the lasertable of the “UNIVERSAL LASER SYSTEMS” apparatus (Model No. M300 with45-watt laser), in order to utilize the adjustable z-axis of theapparatus to provide an accurate measurement of the distance of thelaser nozzle to the surface of the tape. (This laser has a conicalnozzle, through which the laser beam and a stream of compressed airpass. These features clear the optical components of any molten debrisand assist in the laser burning operation. The dimensions described inthis test are relative to the tip of the nozzle, and, consequently, theeffect of the nozzle on the size of the opening formed should beconsidered when determining optimum placement of the tape relative tothe laser apparatus.) No other function of the aforementioned apparatuswas used. The tape was set to contact the aperture of the laser. Theopenings in the tape of the first split were made in this condition. Thetable of the apparatus was then lowered in increments of 0.3 mm toproduce a split at each table movement. This movement was continueduntil no opening could be measured. The tape speed was 6 meters perminute, the frequency was 200 Hz, and the duty cycle was 10% to providea 0.5 ms pulse width.

After each batch of splits had been produced, the samples were measuredon the “Mitutoyo Quick Vision PRO” analyzer. Fifty cells from each splitwere measured for diameter of openings and intervals between openings.This data was imported into an Excel spreadsheet and manipulated toproduce graphs (not included) for the various results. The average forthe 50 cells measured was taken as the data point for the split andpresented on a graph (not included).

The size of the openings formed in the tape decreased as laser powerdropped, everything else remaining constant. The size of the openingsformed in the tape decreased as the duty cycle decreased, everythingelse remaining constant. Other parameters were not significantlyaffected by changes in (a) the level of power used by the laser, (b) thespeed of the tape used in the process of forming openings in the tape,or (c) the duty cycle of the laser. For example, the intervals betweenopenings were not significantly affected except at very low powerlevels. As a further example, the intervals between the openings werenot significantly affected by changes by speed of the tape used in theprocess of forming openings in the tape.

At 0 mm the beam was out of focus, and, consequently, burned largeropenings as the beam covered a larger area. When the tape was at adistance of 2 mm from the aperture of the laser, the tape was in theoptimum position, yielding an opening size of 0.15 mm, which remainedconstant in a range of 1.5 to 2.5 mm from the nozzle. As the tape movedfurther away from the nozzle of the laser, the beam widened until theenergy generated did not penetrate through the tape.

Example 7

The purpose of this example was to determine the capabilities of a laserapparatus for forming openings in a tape. The example also assessed theaccuracy of the positioning of the openings relative to an edge of thetape.

The following settings were used to create the vent openings in the tapeused to prepare the covers of the biosensor strips.

TABLE IV Setting Value Laser Table Coordinates X-coordinate 230.7Y-coordinate 75.56 Power setting 20% Lens type 1.5 inch focal lengthFocus length 11 mm Tape handling rig drive 10.5 volts Tape handling rigrewind 30 volts Tape handling rig shutter 0.9 voltsThree reels of tape were processed to determine if any differences couldbe created from the set-up of the laser perforating apparatus. Tapes(MediSense part number R11003, 15 mm wide) were placed on the apparatusand run through the settings set forth in TABLE IV. Each tape was thenremoved and ten 300 mm lengths were cut at random intervals along thelength. The samples were than analyzed by means of the “Mitutoyo QuickVision PRO” analyzer to measure the accuracy and repeatability of thelaser apparatus.

The “Mitutoyo Quick Vision PRO” analyzer was programmed to search for afirst edge of the tape and measure four points along the surface at 50mm intervals. The system then placed a straight line through thesepoints, which line became the datum line. The center opening positionswere measured from this datum line. The process was repeated for allthree reels. The “Mitutoyo Quick Vision PRO” analyzer measured theintervals between the openings, the diameters of the openings, and thedistances from the centers of the openings to the first edge of the tapeof 100 openings on the 300 mm long samples.

Tables V-VIII set forth the results of pooled data from each of Reels 1,2 and 3, and the pooled data from the combination of the pooled data ofReels 1, 2 and 3. Tables V-VII shows the pooled results for the creationof 10 openings. Units of measurement in TABLES V-VIII are inmillimeters, except for % CV.

TABLE V shows the pooled data from the 10 samples of Reel 1.

TABLE V Interval Distance Diameter Average 1.067 3.800 0.364 SD 0.0370.030 0.021 % CV 3.449 0.777 5.896 Maximum 1.176 3.871 0.488 Minimum0.926 3.710 0.199 Variance 0.250 0.161 0.290TABLE VII shows the pooled data from the 10 samples of Reel 2

TABLE VI Interval Distance Diameter Average 0.998 3.904 0.362 SD 0.0400.021 0.017 % CV 4.004 0.532 4.708 Maximum 1.160 3.960 0.474 Minimum0.914 3.821 0.310 Variance 0.245 0.139 0.164TABLE VII shows the pooled data from the 10 samples of Reel 3.

TABLE VII Interval Distance Diameter Average 1.027 4.060 0.357 SD 0.0320.024 0.015 % CV 3.149 0.588 4.146 Maximum 1.139 4.124 0.434 Minimum0.937 3.983 0.238 Variance 0.202 0.140 0.196TABLE VIII shows the combined and summarized data for Reels 1, 2 and 3.

TABLE VIII Interval Distance Diameter Average 1.031 3.922 0.361 SD 0.0460.110 0.018 % CV 4.497 2.797 5.033 Maximum 1.176 4.124 0.488 Minimum0.914 3.710 0.199 Variance 0.261 0.414 0.290The interval changes by about 0.03 mm between reels. This variation isextremely small and is most likely attributable to variations in speedof the tape or shutter drive system. The average distance of theopenings from the first edge of the tape of the reels varied by about0.2 mm. This result may be due to variations in width in the slitting ofthe tape, resulting from the way in which the tapes were guided on theapparatus. This variation would directly affect the position of theopenings. The variation in the diameter of the opening was very small.The results were very good. The results indicate that the specificationsfor forming openings by means of a laser would be achievable. Thesespecifications are as follows:

Diameter of opening: 0.05 to 0.3 mm±0.03 mm

Interval between openings: 0.3 to 6 mm±0.03 mm

Distance from edge: 0.5 to 20 mm±0.05 mm

If the focal point of the laser is altered, the diameter of the openingcan be increased or decreased. Varying the speed of the rotating shuttervaries the intervals between the openings.

Example 8

The purpose of this example was to determine the effect on burr size ofopenings formed by a laser as a function of the direction of burning theopenings. The tape has an initial thickness. When the laser forms anopening, much of the material that is removed is expelled as vapor.However, some of this material merely moves laterally, therebyincreasing the thickness of the material surrounding the opening. Suchburrs tend to be unsightly.

Two samples were produced on prototype laser perforation equipment asdescribed below.

Green lidding tape, MediSense part number R11003, was used for thisexample. The tape was a plastic tape, having a polyester backing havinga hot melt adhesive coated on one major surface thereof.

The apparatus was cleaned prior to each production of samples. The firstroll (sample 1) was perforated from the backing side of the tape. Thesecond roll (sample 2) was perforated from the adhesive side of thetape. The laser apparatus (“UNIVERSAL LASER SYSTEMS” Model M300)employed the same settings for both samples, which were as follows.

Laser power 85% Shutter speed  3.2 volts Speed of nip rollers 30.2 voltsRewind speed   24 volts

Approximately 20 meters of each tape were produced for testing.

One sample section of tape was taken from each of the two rolls andscanned on both major surfaces by means of a “PROSCAN” profilometer.Five openings from each scan were measured using the “PROSCAN” softwaresectioning tool. Each opening was measured at four positions:

1. The land at the top of the opening

2. The peak of the burr on one side (top) of the opening

3. The peak of the burr on the other side (top) of the opening

4. The land at the bottom of the opening

FIG. 13 shows the measurement points.

Table IX summarizes the results of forming the openings in Roll 1 byperforating tape from the backing side of the tape and scanning from theadhesive side of the tape. Table X summarizes the results of forming theopenings in Roll 1 by perforating tape from the backing side of the tapeand scanning from the backing side of the tape. Table XI summarizes theresults of forming the openings in Roll 2 by perforating tape from theadhesive side of the tape and scanning from the adhesive side of thetape. Table XII summarizes the results of forming the openings byperforating tape from the adhesive side of the tape and scanning fromthe backing side of the tape. The average of points 1 and 4 weresubtracted from the average of points 2 and 3 to give the burr size forthe opening under examination. The average of the five openings measuredper sample was taken as the burr size for that side of the sample oftape (i.e., backing side, adhesive side). Burr sizes from each side ofthe tape (i.e., backing side, adhesive side) were added together to givean overall burr size for the sample of tape. The values in TABLES IX-XIIare in micrometers.

The results in Tables IX and X involve tape that that was perforatedfrom the backing side of the tape. The data in Table IX are for a scanof the adhesive side of the tape.

TABLE IX Open- Open- Open- Open- ing 1 ing 2 ing 3 ing 4 Opening 5Measurement 1 50.64 51.84 52.26 48.39 55.22 Measurement 2 58.15 57.8859.18 56.47 60.80 Measurement 3 54.76 59.90 60.41 58.46 60.87Measurement 4 46.91 48.72 47.40 53.19 50.68 Burr Size 7.68 8.61 9.966.67 7.88 8.16

The data in Table X are for a scan of the backing side of the tape.

TABLE X Open- Open- Open- Open- ing 1 ing 2 ing 3 ing 4 Opening 5Measurement 1 63.53 54.85 47.23 43.67 45.91 Measurement 2 77.13 71.4362.80 58.59 55.55 Measurement 3 75.74 69.73 62.96 55.55 55.41Measurement 4 63.72 56.05 48.77 43.80 44.56 Burr Size 12.81 15.13 14.8813.36 10.24 13.27

The results in Tables XI and XII involve tape that that was perforatedfrom the adhesive side of the tape. The data in Table XII are for a scanof the adhesive side of the tape.

TABLE XI Open- Open- Open- Open- ing 1 ing 2 ing 3 ing 4 Opening 5Measurement 1 60.71 55.66 51.75 50.21 45.58 Measurement 2 78.30 72.6568.3 67.03 62.01 Measurement 3 75.90 72.74 71.22 69.23 65.43 Measurement4 55.66 55.16 52.37 51.44 47.86 Burr Size 18.92 16.78 17.7 17.3 17.017.54

The data in Table XII are for a scan of the backing side of the tape.

TABLE XII Open- Open- Open- Open- ing 1 ing 2 ing 3 ing 4 Opening 5Measurement 1 54.48 52.88 52.76 52.32 49.98 Measurement 2 60.76 60.0760.51 60.17 56.96 Measurement 3 64.16 60.12 59.93 67.46 59.61Measurement 4 51.52 49.97 48.64 48.32 48.29 Burr Size 9.46 8.67 9.5213.49 9.15 10.05

Regardless of the direction from which the tape is perforated, the burris skewed towards the laser source. The larger crater/burr forms on theside of the tape facing of the laser beam due to that side's beingexposed to the heat for a longer time, and inability of the meltedmaterial to be displaced to the opposite side of the tape as the beam isstill trying to break through to create the opening.

From the results, it can be said that perforation from the backing sidecauses less of a burr on the tape surface, albeit a difference of 6.16micrometers, which is still a reduction of 25%. The direction of theperforation has an effect on the distribution of the burr between thetwo sides of the tape. It seems likely that perforation from the backingside through to the adhesive side is preferable.

Various modifications and alterations of this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure, and it should be understood that thisdisclosure is not to be unduly limited to the illustrative embodimentsset forth herein.

1. A method of determining the concentration of an analyte in a sample,the method comprising: contacting the sample with a biosensor, whereinthe biosensor comprises: a spacer layer that provides a sample chamberbetween an electrode support and a cover, the sample chamber comprisinga proximal end where the sample is introduced into the sample chamberand a distal end toward which the sample flows, wherein at least aportion of an electrode arrangement is located within the samplechamber, and wherein an incompressible element placed in-between saidcover and said spacer layer provides at least one vent in the samplechamber, wherein the incompressible element is positioned only at thedistal end of the sample chamber or only near the distal end of thesample chamber; wherein said biosensor is configured to determine theconcentration of an analyte in said sample.
 2. The method of claim 1,wherein the sample chamber has a volume of no more than about 1microliter.
 3. The method of claim 1, wherein the incompressible elementprovides two vents in the sample chamber.
 4. The method of claim 1,wherein the at least one vent is located in a distal end of the samplechamber.
 5. The method of claim 1, wherein the incompressible element isselected from the group consisting of at least one filament, at leastone thread, at least one ribbon, and at least one tape.
 6. The method ofclaim 1, wherein the biosensor comprises at least one layer of meshinterposed between said cover and said electrode arrangement.
 7. Themethod of claim 6, wherein the at least one layer of mesh comprisespolyester.
 8. The method of claim 6, wherein the at least one layer ofmesh comprises a surfactant thereon.
 9. The method of claim 1, whereinthe cover of said biosensor comprises a backing having a layer of anadhesive on one major surface thereof.
 10. The method of claim 9,wherein said adhesive is a pressure-sensitive adhesive.
 11. The methodof claim 9, wherein said adhesive is a hot melt adhesive.
 12. The methodof claim 1, wherein the volume of the sample chamber of said biosensoris no more than about 0.5 microliters.
 13. The method of claim 1,wherein the volume of the sample chamber of said biosensor is no morethan about 0.3 microliters.
 14. The method of claim 1, wherein thevolume of the sample chamber of said biosensor is no more than about 0.2microliters.
 15. The method of claim 1, wherein the volume of the samplechamber of said biosensor is no more than about 0.1 microliters.
 16. Themethod of claim 1, wherein said biosensor is configured to determine theconcentration of the analyte in about 5-10 seconds.
 17. The method ofclaim 1, wherein said biosensor is configured to determine theconcentration of the analyte in about 3-5 seconds.
 18. The method ofclaim 1, wherein said biosensor is configured to determine theconcentration of the analyte in about 1-3 seconds.
 19. The method ofclaim 1, wherein the analyte in said sample is glucose.
 20. The methodof claim 1, wherein the electrode support of said biosensor has aplurality of openings formed therein, wherein at least one of saidopenings is in register with said sample chamber.
 21. The method ofclaim 1, wherein the cover of said biosensor has a plurality of openingsformed therein, wherein at least one of said openings is in registerwith said sample chamber.
 22. The method of claim 1, wherein theincompressible element is a filament or a thread.
 23. The method ofclaim 1, wherein the incompressible element is constructed of asubstantially hydrophobic material.